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 $55.95   3.614%   $57.972   $57.97   $57.95   $58.00  
  Purchase #2 $117.77   7.427%   $126.5168   $126.52   $126.50   $126.50  
  Purchase #3 $228.79   11.832%   $255.8604   $255.86   $255.85   $255.90  
  Purchase #4 $222.36   4.871%   $233.1912   $233.19   $233.20   $233.20  
  Purchase #5 $213.68   8.577%   $232.0073   $232.01   $232.00   $232.00  
  Purchase #6 $14.59   12.758%   $16.4514   $16.45   $16.45   $16.50  
  Purchase #7 $46.25   4.184%   $48.1851   $48.19   $48.20   $48.20  
  7 purchase totals = $899.39       $970.1842   $970.19   $970.15   $970.30