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 $43.91   7.466%   $47.1883   $47.19   $47.20   $47.20  
  Purchase #2 $85.38   8.516%   $92.651   $92.65   $92.65   $92.70  
  Purchase #3 $205.68   11.722%   $229.7898   $229.79   $229.80   $229.80  
  Purchase #4 $75.99   8.513%   $82.459   $82.46   $82.45   $82.50  
  Purchase #5 $62.98   11.775%   $70.3959   $70.40   $70.40   $70.40  
  Purchase #6 $19.65   5.441%   $20.7192   $20.72   $20.70   $20.70  
  Purchase #7 $188.52   7.683%   $203.004   $203.00   $203.00   $203.00  
  7 purchase totals = $682.11       $746.2072   $746.21   $746.20   $746.30