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 $52.72   13.232%   $59.6959   $59.70   $59.70   $59.70  
  Purchase #2 $224.96   9.293%   $245.8655   $245.87   $245.85   $245.90  
  Purchase #3 $55.82   5.515%   $58.8985   $58.90   $58.90   $58.90  
  Purchase #4 $244.99   5.404%   $258.2293   $258.23   $258.25   $258.20  
  Purchase #5 $233.69   8.458%   $253.4555   $253.46   $253.45   $253.50  
  Purchase #6 $38.58   11.439%   $42.9932   $42.99   $43.00   $43.00  
  Purchase #7 $125.70   5.484%   $132.5934   $132.59   $132.60   $132.60  
  7 purchase totals = $976.46       $1,051.7313   $1,051.74   $1,051.75   $1,051.80