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 $148.32   8.578%   $161.0429   $161.04   $161.05   $161.00  
  Purchase #2 $78.89   8.170%   $85.3353   $85.34   $85.35   $85.30  
  Purchase #3 $86.68   8.263%   $93.8424   $93.84   $93.85   $93.80  
  Purchase #4 $87.61   7.509%   $94.1886   $94.19   $94.20   $94.20  
  Purchase #5 $193.78   3.824%   $201.1901   $201.19   $201.20   $201.20  
  Purchase #6 $149.38   6.699%   $159.387   $159.39   $159.40   $159.40  
  Purchase #7 $59.66   11.568%   $66.5615   $66.56   $66.55   $66.60  
  7 purchase totals = $804.32       $861.5478   $861.55   $861.60   $861.50