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 $178.82   13.522%   $203   $203.00   $203.00   $203.00  
  Purchase #2 $158.79   3.760%   $164.7605   $164.76   $164.75   $164.80  
  Purchase #3 $163.27   10.531%   $180.464   $180.46   $180.45   $180.50  
  Purchase #4 $208.90   13.535%   $237.1746   $237.17   $237.15   $237.20  
  Purchase #5 $242.58   11.834%   $271.2869   $271.29   $271.30   $271.30  
  Purchase #6 $23.87   6.323%   $25.3793   $25.38   $25.40   $25.40  
  Purchase #7 $218.80   5.249%   $230.2848   $230.28   $230.30   $230.30  
  7 purchase totals = $1,195.03       $1,312.3501   $1,312.34   $1,312.35   $1,312.50