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 $237.58   12.506%   $267.2918   $267.29   $267.30   $267.30  
  Purchase #2 $106.95   13.241%   $121.1112   $121.11   $121.10   $121.10  
  Purchase #3 $231.73   3.805%   $240.5473   $240.55   $240.55   $240.50  
  Purchase #4 $202.41   8.122%   $218.8497   $218.85   $218.85   $218.80  
  Purchase #5 $127.70   4.464%   $133.4005   $133.40   $133.40   $133.40  
  Purchase #6 $37.98   10.663%   $42.0298   $42.03   $42.05   $42.00  
  Purchase #7 $8.86   4.227%   $9.2345   $9.23   $9.25   $9.20  
  7 purchase totals = $953.21       $1,032.4648   $1,032.46   $1,032.50   $1,032.30