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 $86.45   8.756%   $94.0196   $94.02   $94.00   $94.00  
  Purchase #2 $182.67   13.249%   $206.8719   $206.87   $206.85   $206.90  
  Purchase #3 $27.64   10.498%   $30.5416   $30.54   $30.55   $30.50  
  Purchase #4 $130.27   12.592%   $146.6736   $146.67   $146.65   $146.70  
  Purchase #5 $9.63   12.394%   $10.8235   $10.82   $10.80   $10.80  
  Purchase #6 $68.70   4.827%   $72.0161   $72.02   $72.00   $72.00  
  Purchase #7 $142.51   5.608%   $150.502   $150.50   $150.50   $150.50  
  7 purchase totals = $647.87       $711.4483   $711.44   $711.35   $711.40