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 $244.76   12.591%   $275.5777   $275.58   $275.60   $275.60  
  Purchase #2 $214.93   5.541%   $226.8393   $226.84   $226.85   $226.80  
  Purchase #3 $117.67   11.813%   $131.5704   $131.57   $131.55   $131.60  
  Purchase #4 $31.66   5.416%   $33.3747   $33.37   $33.35   $33.40  
  Purchase #5 $110.68   12.382%   $124.3844   $124.38   $124.40   $124.40  
  Purchase #6 $95.74   11.271%   $106.5309   $106.53   $106.55   $106.50  
  Purchase #7 $188.90   13.406%   $214.2239   $214.22   $214.20   $214.20  
  7 purchase totals = $1,004.34       $1,112.5013   $1,112.49   $1,112.50   $1,112.50