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 $173.26   5.263%   $182.3787   $182.38   $182.40   $182.40  
  Purchase #2 $221.57   11.638%   $247.3563   $247.36   $247.35   $247.40  
  Purchase #3 $12.62   7.414%   $13.5556   $13.56   $13.55   $13.60  
  Purchase #4 $115.47   9.565%   $126.5147   $126.51   $126.50   $126.50  
  Purchase #5 $231.50   9.853%   $254.3097   $254.31   $254.30   $254.30  
  Purchase #6 $191.60   5.676%   $202.4752   $202.48   $202.50   $202.50  
  Purchase #7 $218.56   9.201%   $238.6697   $238.67   $238.65   $238.70  
  7 purchase totals = $1,164.58       $1,265.2599   $1,265.27   $1,265.25   $1,265.40