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 $111.69   5.793%   $118.1602   $118.16   $118.15   $118.20  
  Purchase #2 $204.61   10.771%   $226.6485   $226.65   $226.65   $226.60  
  Purchase #3 $236.92   9.231%   $258.7901   $258.79   $258.80   $258.80  
  Purchase #4 $71.59   6.102%   $75.9584   $75.96   $75.95   $76.00  
  Purchase #5 $26.95   6.144%   $28.6058   $28.61   $28.60   $28.60  
  Purchase #6 $46.85   10.194%   $51.6259   $51.63   $51.65   $51.60  
  Purchase #7 $42.94   10.134%   $47.2915   $47.29   $47.30   $47.30  
  7 purchase totals = $741.55       $807.0804   $807.09   $807.10   $807.10