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 $237.27   6.752%   $253.2905   $253.29   $253.30   $253.30  
  Purchase #2 $14.95   13.860%   $17.0221   $17.02   $17.00   $17.00  
  Purchase #3 $223.79   11.302%   $249.0827   $249.08   $249.10   $249.10  
  Purchase #4 $108.82   13.752%   $123.7849   $123.78   $123.80   $123.80  
  Purchase #5 $186.44   7.333%   $200.1116   $200.11   $200.10   $200.10  
  Purchase #6 $54.62   7.205%   $58.5554   $58.56   $58.55   $58.60  
  Purchase #7 $135.25   5.580%   $142.797   $142.80   $142.80   $142.80  
  7 purchase totals = $961.14       $1,044.6442   $1,044.64   $1,044.65   $1,044.70