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 $200.82   12.685%   $226.294   $226.29   $226.30   $226.30  
  Purchase #2 $115.59   11.253%   $128.5973   $128.60   $128.60   $128.60  
  Purchase #3 $160.58   9.223%   $175.3903   $175.39   $175.40   $175.40  
  Purchase #4 $136.85   8.214%   $148.0909   $148.09   $148.10   $148.10  
  Purchase #5 $63.55   12.869%   $71.7282   $71.73   $71.75   $71.70  
  Purchase #6 $70.68   5.452%   $74.5335   $74.53   $74.55   $74.50  
  Purchase #7 $157.38   10.583%   $174.0355   $174.04   $174.05   $174.00  
  7 purchase totals = $905.45       $998.6697   $998.67   $998.75   $998.60