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 $116.46   13.427%   $132.0971   $132.10   $132.10   $132.10  
  Purchase #2 $105.31   11.829%   $117.7671   $117.77   $117.75   $117.80  
  Purchase #3 $238.28   7.401%   $255.9151   $255.92   $255.90   $255.90  
  Purchase #4 $45.57   6.250%   $48.4181   $48.42   $48.40   $48.40  
  Purchase #5 $234.88   10.744%   $260.1155   $260.12   $260.10   $260.10  
  Purchase #6 $182.93   5.200%   $192.4424   $192.44   $192.45   $192.40  
  Purchase #7 $13.69   13.575%   $15.5484   $15.55   $15.55   $15.50  
  7 purchase totals = $937.12       $1,022.3037   $1,022.32   $1,022.25   $1,022.20