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 $85.91   8.465%   $93.1823   $93.18   $93.20   $93.20  
  Purchase #2 $234.91   9.806%   $257.9453   $257.95   $257.95   $257.90  
  Purchase #3 $231.42   11.647%   $258.3735   $258.37   $258.35   $258.40  
  Purchase #4 $157.58   11.683%   $175.9901   $175.99   $176.00   $176.00  
  Purchase #5 $41.93   3.586%   $43.4336   $43.43   $43.45   $43.40  
  Purchase #6 $16.90   12.537%   $19.0188   $19.02   $19.00   $19.00  
  Purchase #7 $189.87   13.726%   $215.9316   $215.93   $215.95   $215.90  
  7 purchase totals = $958.52       $1,063.8752   $1,063.87   $1,063.90   $1,063.80