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 $45.33   9.588%   $49.6762   $49.68   $49.70   $49.70  
  Purchase #2 $60.87   10.731%   $67.402   $67.40   $67.40   $67.40  
  Purchase #3 $70.77   7.369%   $75.985   $75.99   $76.00   $76.00  
  Purchase #4 $119.43   8.448%   $129.5194   $129.52   $129.50   $129.50  
  Purchase #5 $116.33   11.358%   $129.5428   $129.54   $129.55   $129.50  
  Purchase #6 $88.62   5.361%   $93.3709   $93.37   $93.35   $93.40  
  Purchase #7 $250.38   12.701%   $282.1808   $282.18   $282.20   $282.20  
  7 purchase totals = $751.73       $827.6771   $827.68   $827.70   $827.70