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 $184.77   5.451%   $194.8418   $194.84   $194.85   $194.80  
  Purchase #2 $167.68   9.736%   $184.0053   $184.01   $184.00   $184.00  
  Purchase #3 $195.84   13.557%   $222.39   $222.39   $222.40   $222.40  
  Purchase #4 $68.27   11.439%   $76.0794   $76.08   $76.10   $76.10  
  Purchase #5 $95.29   13.776%   $108.4172   $108.42   $108.40   $108.40  
  Purchase #6 $183.85   11.534%   $205.0553   $205.06   $205.05   $205.10  
  Purchase #7 $75.46   8.781%   $82.0861   $82.09   $82.10   $82.10  
  7 purchase totals = $971.16       $1,072.8751   $1,072.89   $1,072.90   $1,072.90