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 $61.38   8.554%   $66.6304   $66.63   $66.65   $66.60  
  Purchase #2 $174.42   12.388%   $196.0271   $196.03   $196.05   $196.00  
  Purchase #3 $181.52   4.515%   $189.7156   $189.72   $189.70   $189.70  
  Purchase #4 $218.53   7.484%   $234.8848   $234.88   $234.90   $234.90  
  Purchase #5 $107.98   9.471%   $118.2068   $118.21   $118.20   $118.20  
  Purchase #6 $183.38   12.469%   $206.2457   $206.25   $206.25   $206.20  
  Purchase #7 $216.66   9.493%   $237.2275   $237.23   $237.25   $237.20  
  7 purchase totals = $1,143.87       $1,248.9379   $1,248.95   $1,249.00   $1,248.80