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 $126.91   3.616%   $131.4991   $131.50   $131.50   $131.50  
  Purchase #2 $237.44   12.155%   $266.3008   $266.30   $266.30   $266.30  
  Purchase #3 $58.34   10.158%   $64.2662   $64.27   $64.25   $64.30  
  Purchase #4 $62.94   8.596%   $68.3503   $68.35   $68.35   $68.40  
  Purchase #5 $218.92   3.819%   $227.2806   $227.28   $227.30   $227.30  
  Purchase #6 $119.41   5.487%   $125.962   $125.96   $125.95   $126.00  
  Purchase #7 $50.45   12.678%   $56.8461   $56.85   $56.85   $56.80  
  7 purchase totals = $874.41       $940.5051   $940.51   $940.50   $940.60