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 $207.32   13.140%   $234.5618   $234.56   $234.55   $234.60  
  Purchase #2 $57.74   11.304%   $64.2669   $64.27   $64.25   $64.30  
  Purchase #3 $203.69   6.184%   $216.2862   $216.29   $216.30   $216.30  
  Purchase #4 $184.97   12.834%   $208.709   $208.71   $208.70   $208.70  
  Purchase #5 $57.33   12.169%   $64.3065   $64.31   $64.30   $64.30  
  Purchase #6 $176.72   13.684%   $200.9024   $200.90   $200.90   $200.90  
  Purchase #7 $236.90   7.729%   $255.21   $255.21   $255.20   $255.20  
  7 purchase totals = $1,124.67       $1,244.2428   $1,244.25   $1,244.20   $1,244.30