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 $68.57   12.477%   $77.1255   $77.13   $77.15   $77.10  
  Purchase #2 $198.71   10.135%   $218.8493   $218.85   $218.85   $218.80  
  Purchase #3 $84.54   13.433%   $95.8963   $95.90   $95.90   $95.90  
  Purchase #4 $99.61   9.353%   $108.9265   $108.93   $108.95   $108.90  
  Purchase #5 $61.86   13.372%   $70.1319   $70.13   $70.15   $70.10  
  Purchase #6 $73.87   3.467%   $76.4311   $76.43   $76.45   $76.40  
  Purchase #7 $6.46   7.366%   $6.9358   $6.94   $6.95   $6.90  
  7 purchase totals = $593.62       $654.2964   $654.31   $654.40   $654.10