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 $187.82   9.127%   $204.9623   $204.96   $204.95   $205.00  
  Purchase #2 $168.68   7.337%   $181.0561   $181.06   $181.05   $181.10  
  Purchase #3 $225.61   13.534%   $256.1441   $256.14   $256.15   $256.10  
  Purchase #4 $120.43   3.726%   $124.9172   $124.92   $124.90   $124.90  
  Purchase #5 $94.97   13.277%   $107.5792   $107.58   $107.60   $107.60  
  Purchase #6 $234.87   13.258%   $266.0091   $266.01   $266.00   $266.00  
  Purchase #7 $34.28   6.458%   $36.4938   $36.49   $36.50   $36.50  
  7 purchase totals = $1,066.66       $1,177.1618   $1,177.16   $1,177.15   $1,177.20