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 $49.79   9.619%   $54.5793   $54.58   $54.60   $54.60  
  Purchase #2 $247.80   6.750%   $264.5265   $264.53   $264.55   $264.50  
  Purchase #3 $94.78   3.534%   $98.1295   $98.13   $98.15   $98.10  
  Purchase #4 $64.56   9.201%   $70.5002   $70.50   $70.50   $70.50  
  Purchase #5 $197.99   7.223%   $212.2908   $212.29   $212.30   $212.30  
  Purchase #6 $106.83   5.356%   $112.5518   $112.55   $112.55   $112.60  
  Purchase #7 $33.26   10.169%   $36.6422   $36.64   $36.65   $36.60  
  7 purchase totals = $795.01       $849.2203   $849.22   $849.30   $849.20