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 $211.82   9.799%   $232.5762   $232.58   $232.60   $232.60  
  Purchase #2 $12.90   4.254%   $13.4488   $13.45   $13.45   $13.40  
  Purchase #3 $25.77   10.458%   $28.465   $28.47   $28.45   $28.50  
  Purchase #4 $222.55   9.588%   $243.8881   $243.89   $243.90   $243.90  
  Purchase #5 $121.77   3.786%   $126.3802   $126.38   $126.40   $126.40  
  Purchase #6 $230.54   4.559%   $241.0503   $241.05   $241.05   $241.10  
  Purchase #7 $60.69   10.677%   $67.1699   $67.17   $67.15   $67.20  
  7 purchase totals = $886.04       $952.9785   $952.99   $953.00   $953.10