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 $219.33   7.123%   $234.9529   $234.95   $234.95   $235.00  
  Purchase #2 $38.96   11.189%   $43.3192   $43.32   $43.30   $43.30  
  Purchase #3 $238.93   11.823%   $267.1787   $267.18   $267.20   $267.20  
  Purchase #4 $75.58   7.806%   $81.4798   $81.48   $81.50   $81.50  
  Purchase #5 $161.39   9.511%   $176.7398   $176.74   $176.75   $176.70  
  Purchase #6 $58.83   6.183%   $62.4675   $62.47   $62.45   $62.50  
  Purchase #7 $191.43   12.551%   $215.4564   $215.46   $215.45   $215.50  
  7 purchase totals = $984.45       $1,081.5943   $1,081.60   $1,081.60   $1,081.70