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 $47.81   10.670%   $52.9113   $52.91   $52.90   $52.90  
  Purchase #2 $167.89   5.605%   $177.3002   $177.30   $177.30   $177.30  
  Purchase #3 $69.76   8.647%   $75.7921   $75.79   $75.80   $75.80  
  Purchase #4 $32.68   9.766%   $35.8715   $35.87   $35.85   $35.90  
  Purchase #5 $92.59   5.737%   $97.9019   $97.90   $97.90   $97.90  
  Purchase #6 $91.55   10.869%   $101.5006   $101.50   $101.50   $101.50  
  Purchase #7 $161.44   12.301%   $181.2987   $181.30   $181.30   $181.30  
  7 purchase totals = $663.72       $722.5763   $722.57   $722.55   $722.60