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 $249.36   13.168%   $282.1957   $282.20   $282.20   $282.20  
  Purchase #2 $189.92   4.234%   $197.9612   $197.96   $197.95   $198.00  
  Purchase #3 $118.38   13.703%   $134.6016   $134.60   $134.60   $134.60  
  Purchase #4 $27.78   5.497%   $29.3071   $29.31   $29.30   $29.30  
  Purchase #5 $204.25   11.856%   $228.4659   $228.47   $228.45   $228.50  
  Purchase #6 $160.48   4.874%   $168.3018   $168.30   $168.30   $168.30  
  Purchase #7 $71.73   6.600%   $76.4642   $76.46   $76.45   $76.50  
  7 purchase totals = $1,021.90       $1,117.2975   $1,117.30   $1,117.25   $1,117.40