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 $173.33   5.401%   $182.6916   $182.69   $182.70   $182.70  
  Purchase #2 $56.94   13.230%   $64.4732   $64.47   $64.45   $64.50  
  Purchase #3 $126.86   6.107%   $134.6073   $134.61   $134.60   $134.60  
  Purchase #4 $68.89   8.872%   $75.0019   $75.00   $75.00   $75.00  
  Purchase #5 $197.34   6.853%   $210.8637   $210.86   $210.85   $210.90  
  Purchase #6 $21.81   11.646%   $24.35   $24.35   $24.35   $24.40  
  Purchase #7 $163.26   8.228%   $176.693   $176.69   $176.70   $176.70  
  7 purchase totals = $808.43       $868.6807   $868.67   $868.65   $868.80