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 $41.26   13.355%   $46.7703   $46.77   $46.75   $46.80  
  Purchase #2 $113.47   9.802%   $124.5923   $124.59   $124.60   $124.60  
  Purchase #3 $186.89   12.247%   $209.7784   $209.78   $209.80   $209.80  
  Purchase #4 $96.25   10.160%   $106.029   $106.03   $106.05   $106.00  
  Purchase #5 $117.65   12.177%   $131.9762   $131.98   $132.00   $132.00  
  Purchase #6 $162.57   4.751%   $170.2937   $170.29   $170.30   $170.30  
  Purchase #7 $225.72   3.851%   $234.4125   $234.41   $234.40   $234.40  
  7 purchase totals = $943.81       $1,023.8524   $1,023.85   $1,023.90   $1,023.90