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 $244.98   12.598%   $275.8426   $275.84   $275.85   $275.80  
  Purchase #2 $129.41   11.467%   $144.2494   $144.25   $144.25   $144.20  
  Purchase #3 $171.60   13.498%   $194.7626   $194.76   $194.75   $194.80  
  Purchase #4 $144.79   12.812%   $163.3405   $163.34   $163.35   $163.30  
  Purchase #5 $41.40   4.508%   $43.2663   $43.27   $43.25   $43.30  
  Purchase #6 $29.98   5.767%   $31.7089   $31.71   $31.70   $31.70  
  Purchase #7 $43.55   8.352%   $47.1873   $47.19   $47.20   $47.20  
  7 purchase totals = $805.71       $900.3576   $900.36   $900.35   $900.30