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 $92.52   3.642%   $95.8896   $95.89   $95.90   $95.90  
  Purchase #2 $133.73   7.576%   $143.8614   $143.86   $143.85   $143.90  
  Purchase #3 $73.54   10.293%   $81.1095   $81.11   $81.10   $81.10  
  Purchase #4 $96.81   5.832%   $102.456   $102.46   $102.45   $102.50  
  Purchase #5 $141.48   4.775%   $148.2357   $148.24   $148.25   $148.20  
  Purchase #6 $116.99   7.511%   $125.7771   $125.78   $125.80   $125.80  
  Purchase #7 $201.94   13.234%   $228.6647   $228.66   $228.65   $228.70  
  7 purchase totals = $857.01       $925.9940   $926.00   $926.00   $926.10