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 $68.58   10.659%   $75.8899   $75.89   $75.90   $75.90  
  Purchase #2 $239.31   12.271%   $268.6757   $268.68   $268.70   $268.70  
  Purchase #3 $208.45   4.807%   $218.4702   $218.47   $218.45   $218.50  
  Purchase #4 $141.46   10.352%   $156.1039   $156.10   $156.10   $156.10  
  Purchase #5 $78.35   12.698%   $88.2989   $88.30   $88.30   $88.30  
  Purchase #6 $130.50   13.700%   $148.3785   $148.38   $148.40   $148.40  
  Purchase #7 $77.48   4.148%   $80.6939   $80.69   $80.70   $80.70  
  7 purchase totals = $944.13       $1,036.5110   $1,036.51   $1,036.55   $1,036.60