Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $222.39   11.760%   $248.5431   $248.54   $248.55   $248.50  
  Purchase #2 $187.99   8.209%   $203.4221   $203.42   $203.40   $203.40  
  Purchase #3 $182.55   11.209%   $203.012   $203.01   $203.00   $203.00  
  Purchase #4 $111.69   10.560%   $123.4845   $123.48   $123.50   $123.50  
  Purchase #5 $217.26   6.164%   $230.6519   $230.65   $230.65   $230.70  
  Purchase #6 $192.53   5.769%   $203.6371   $203.64   $203.65   $203.60  
  Purchase #7 $232.94   12.740%   $262.6166   $262.62   $262.60   $262.60  
  7 purchase totals = $1,347.35       $1,475.3673   $1,475.36   $1,475.35   $1,475.30