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 $182.45   4.623%   $190.8847   $190.88   $190.90   $190.90  
  Purchase #2 $119.39   3.799%   $123.9256   $123.93   $123.95   $123.90  
  Purchase #3 $63.37   7.755%   $68.2843   $68.28   $68.30   $68.30  
  Purchase #4 $56.74   13.540%   $64.4226   $64.42   $64.40   $64.40  
  Purchase #5 $216.46   5.220%   $227.7592   $227.76   $227.75   $227.80  
  Purchase #6 $151.97   9.861%   $166.9558   $166.96   $166.95   $167.00  
  Purchase #7 $177.75   13.347%   $201.4743   $201.47   $201.45   $201.50  
  7 purchase totals = $968.13       $1,043.7065   $1,043.70   $1,043.70   $1,043.80