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 $58.44   12.558%   $65.7789   $65.78   $65.80   $65.80  
  Purchase #2 $209.76   13.303%   $237.6644   $237.66   $237.65   $237.70  
  Purchase #3 $66.87   6.641%   $71.3108   $71.31   $71.30   $71.30  
  Purchase #4 $218.25   12.706%   $245.9808   $245.98   $246.00   $246.00  
  Purchase #5 $5.43   5.179%   $5.7112   $5.71   $5.70   $5.70  
  Purchase #6 $161.53   13.230%   $182.9004   $182.90   $182.90   $182.90  
  Purchase #7 $228.44   11.383%   $254.4433   $254.44   $254.45   $254.40  
  7 purchase totals = $948.72       $1,063.7898   $1,063.78   $1,063.80   $1,063.80