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 $58.52   11.412%   $65.1983   $65.20   $65.20   $65.20  
  Purchase #2 $80.96   3.269%   $83.6066   $83.61   $83.60   $83.60  
  Purchase #3 $175.50   4.481%   $183.3642   $183.36   $183.35   $183.40  
  Purchase #4 $54.40   8.132%   $58.8238   $58.82   $58.80   $58.80  
  Purchase #5 $134.78   13.161%   $152.5184   $152.52   $152.50   $152.50  
  Purchase #6 $204.54   9.647%   $224.272   $224.27   $224.25   $224.30  
  Purchase #7 $90.71   6.305%   $96.4293   $96.43   $96.45   $96.40  
  7 purchase totals = $799.41       $864.2126   $864.21   $864.15   $864.20