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 $81.38   13.226%   $92.1433   $92.14   $92.15   $92.10  
  Purchase #2 $169.59   5.849%   $179.5093   $179.51   $179.50   $179.50  
  Purchase #3 $250.40   7.121%   $268.231   $268.23   $268.25   $268.20  
  Purchase #4 $177.46   13.555%   $201.5147   $201.51   $201.50   $201.50  
  Purchase #5 $145.36   3.402%   $150.3051   $150.31   $150.30   $150.30  
  Purchase #6 $131.61   11.382%   $146.5899   $146.59   $146.60   $146.60  
  Purchase #7 $228.25   4.441%   $238.3866   $238.39   $238.40   $238.40  
  7 purchase totals = $1,184.05       $1,276.6799   $1,276.68   $1,276.70   $1,276.60