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 $247.78   11.561%   $276.4258   $276.43   $276.45   $276.40  
  Purchase #2 $66.82   7.137%   $71.5889   $71.59   $71.60   $71.60  
  Purchase #3 $120.99   4.362%   $126.2676   $126.27   $126.25   $126.30  
  Purchase #4 $31.77   10.321%   $35.049   $35.05   $35.05   $35.00  
  Purchase #5 $73.30   7.702%   $78.9456   $78.95   $78.95   $78.90  
  Purchase #6 $228.73   9.799%   $251.1433   $251.14   $251.15   $251.10  
  Purchase #7 $67.96   8.349%   $73.634   $73.63   $73.65   $73.60  
  7 purchase totals = $837.35       $913.0542   $913.06   $913.10   $912.90