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 $54.87   5.574%   $57.9285   $57.93   $57.95   $57.90  
  Purchase #2 $84.73   11.464%   $94.4434   $94.44   $94.45   $94.40  
  Purchase #3 $99.35   8.398%   $107.6934   $107.69   $107.70   $107.70  
  Purchase #4 $94.61   7.305%   $101.5213   $101.52   $101.50   $101.50  
  Purchase #5 $123.93   12.127%   $138.959   $138.96   $138.95   $139.00  
  Purchase #6 $190.25   6.193%   $202.0322   $202.03   $202.05   $202.00  
  Purchase #7 $240.92   7.700%   $259.4708   $259.47   $259.45   $259.50  
  7 purchase totals = $888.66       $962.0486   $962.04   $962.05   $962.00