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 $184.47   12.834%   $208.1449   $208.14   $208.15   $208.10  
  Purchase #2 $217.45   13.154%   $246.0534   $246.05   $246.05   $246.10  
  Purchase #3 $57.60   4.399%   $60.1338   $60.13   $60.15   $60.10  
  Purchase #4 $95.39   9.463%   $104.4168   $104.42   $104.40   $104.40  
  Purchase #5 $149.84   5.163%   $157.5762   $157.58   $157.60   $157.60  
  Purchase #6 $60.66   9.847%   $66.6332   $66.63   $66.65   $66.60  
  Purchase #7 $235.60   5.669%   $248.9562   $248.96   $248.95   $249.00  
  7 purchase totals = $1,001.01       $1,091.9145   $1,091.91   $1,091.95   $1,091.90