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 $62.71   8.757%   $68.2015   $68.20   $68.20   $68.20  
  Purchase #2 $179.39   12.827%   $202.4004   $202.40   $202.40   $202.40  
  Purchase #3 $238.30   3.415%   $246.4379   $246.44   $246.45   $246.40  
  Purchase #4 $247.56   3.858%   $257.1109   $257.11   $257.10   $257.10  
  Purchase #5 $92.61   3.534%   $95.8828   $95.88   $95.90   $95.90  
  Purchase #6 $53.60   6.181%   $56.913   $56.91   $56.90   $56.90  
  Purchase #7 $132.96   6.317%   $141.3591   $141.36   $141.35   $141.40  
  7 purchase totals = $1,007.13       $1,068.3056   $1,068.30   $1,068.30   $1,068.30