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 $62.78   8.263%   $67.9675   $67.97   $67.95   $68.00  
  Purchase #2 $194.36   5.799%   $205.6309   $205.63   $205.65   $205.60  
  Purchase #3 $165.84   11.301%   $184.5816   $184.58   $184.60   $184.60  
  Purchase #4 $86.28   10.439%   $95.2868   $95.29   $95.30   $95.30  
  Purchase #5 $172.91   11.568%   $192.9122   $192.91   $192.90   $192.90  
  Purchase #6 $69.44   9.566%   $76.0826   $76.08   $76.10   $76.10  
  Purchase #7 $146.26   5.555%   $154.3847   $154.38   $154.40   $154.40  
  7 purchase totals = $897.87       $976.8463   $976.84   $976.90   $976.90