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 $141.56   5.155%   $148.8574   $148.86   $148.85   $148.90  
  Purchase #2 $232.32   10.548%   $256.8251   $256.83   $256.85   $256.80  
  Purchase #3 $58.96   11.815%   $65.9261   $65.93   $65.95   $65.90  
  Purchase #4 $199.79   8.836%   $217.4434   $217.44   $217.45   $217.40  
  Purchase #5 $81.91   3.779%   $85.0054   $85.01   $85.00   $85.00  
  Purchase #6 $43.75   12.572%   $49.2503   $49.25   $49.25   $49.30  
  Purchase #7 $216.43   9.424%   $236.8264   $236.83   $236.85   $236.80  
  7 purchase totals = $974.72       $1,060.1341   $1,060.15   $1,060.20   $1,060.10