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 $61.76   11.754%   $69.0193   $69.02   $69.00   $69.00  
  Purchase #2 $94.33   5.853%   $99.8511   $99.85   $99.85   $99.90  
  Purchase #3 $46.39   11.677%   $51.807   $51.81   $51.80   $51.80  
  Purchase #4 $150.58   3.753%   $156.2313   $156.23   $156.25   $156.20  
  Purchase #5 $241.32   11.646%   $269.4241   $269.42   $269.40   $269.40  
  Purchase #6 $232.73   11.860%   $260.3318   $260.33   $260.35   $260.30  
  Purchase #7 $73.62   10.442%   $81.3074   $81.31   $81.30   $81.30  
  7 purchase totals = $900.73       $987.9720   $987.97   $987.95   $987.90