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 $188.86   5.344%   $198.9527   $198.95   $198.95   $199.00  
  Purchase #2 $24.38   4.362%   $25.4435   $25.44   $25.45   $25.40  
  Purchase #3 $235.51   5.784%   $249.1319   $249.13   $249.15   $249.10  
  Purchase #4 $79.55   8.538%   $86.342   $86.34   $86.35   $86.30  
  Purchase #5 $174.48   8.706%   $189.6702   $189.67   $189.65   $189.70  
  Purchase #6 $47.39   6.615%   $50.5248   $50.52   $50.50   $50.50  
  Purchase #7 $244.67   6.167%   $259.7588   $259.76   $259.75   $259.80  
  7 purchase totals = $994.84       $1,059.8239   $1,059.81   $1,059.80   $1,059.80