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 $199.36   8.476%   $216.2578   $216.26   $216.25   $216.30  
  Purchase #2 $190.69   10.843%   $211.3665   $211.37   $211.35   $211.40  
  Purchase #3 $69.99   6.559%   $74.5806   $74.58   $74.60   $74.60  
  Purchase #4 $149.80   3.807%   $155.5029   $155.50   $155.50   $155.50  
  Purchase #5 $211.54   4.647%   $221.3703   $221.37   $221.35   $221.40  
  Purchase #6 $60.39   4.864%   $63.3274   $63.33   $63.35   $63.30  
  Purchase #7 $89.40   10.342%   $98.6457   $98.65   $98.65   $98.60  
  7 purchase totals = $971.17       $1,041.0512   $1,041.06   $1,041.05   $1,041.10