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 $204.41   9.216%   $223.2484   $223.25   $223.25   $223.20  
  Purchase #2 $67.63   10.435%   $74.6872   $74.69   $74.70   $74.70  
  Purchase #3 $62.29   10.506%   $68.8342   $68.83   $68.85   $68.80  
  Purchase #4 $165.40   10.247%   $182.3485   $182.35   $182.35   $182.30  
  Purchase #5 $54.63   9.778%   $59.9717   $59.97   $59.95   $60.00  
  Purchase #6 $105.52   10.747%   $116.8602   $116.86   $116.85   $116.90  
  Purchase #7 $64.76   10.680%   $71.6764   $71.68   $71.70   $71.70  
  7 purchase totals = $724.64       $797.6266   $797.63   $797.65   $797.60