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 $78.71   9.282%   $86.0159   $86.02   $86.00   $86.00  
  Purchase #2 $162.46   4.500%   $169.7707   $169.77   $169.75   $169.80  
  Purchase #3 $153.82   8.272%   $166.544   $166.54   $166.55   $166.50  
  Purchase #4 $139.71   9.116%   $152.446   $152.45   $152.45   $152.40  
  Purchase #5 $23.47   7.707%   $25.2788   $25.28   $25.30   $25.30  
  Purchase #6 $34.48   12.597%   $38.8234   $38.82   $38.80   $38.80  
  Purchase #7 $221.58   6.821%   $236.694   $236.69   $236.70   $236.70  
  7 purchase totals = $814.23       $875.5728   $875.57   $875.55   $875.50