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 $67.33   12.513%   $75.755   $75.76   $75.75   $75.80  
  Purchase #2 $88.65   10.294%   $97.7756   $97.78   $97.80   $97.80  
  Purchase #3 $121.50   8.773%   $132.1592   $132.16   $132.15   $132.20  
  Purchase #4 $68.61   4.484%   $71.6865   $71.69   $71.70   $71.70  
  Purchase #5 $61.61   7.464%   $66.2086   $66.21   $66.20   $66.20  
  Purchase #6 $57.60   8.680%   $62.5997   $62.60   $62.60   $62.60  
  Purchase #7 $170.52   6.278%   $181.2252   $181.23   $181.25   $181.20  
  7 purchase totals = $635.82       $687.4098   $687.43   $687.45   $687.50