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 $118.69   11.180%   $131.9595   $131.96   $131.95   $132.00  
  Purchase #2 $81.66   10.839%   $90.5111   $90.51   $90.50   $90.50  
  Purchase #3 $126.74   12.187%   $142.1858   $142.19   $142.20   $142.20  
  Purchase #4 $78.30   5.200%   $82.3716   $82.37   $82.35   $82.40  
  Purchase #5 $5.74   5.534%   $6.0577   $6.06   $6.05   $6.10  
  Purchase #6 $237.62   7.393%   $255.1872   $255.19   $255.20   $255.20  
  Purchase #7 $22.26   13.657%   $25.3   $25.30   $25.30   $25.30  
  7 purchase totals = $671.01       $733.5729   $733.58   $733.55   $733.70