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 $194.29   11.702%   $217.0258   $217.03   $217.05   $217.00  
  Purchase #2 $176.74   5.382%   $186.2521   $186.25   $186.25   $186.30  
  Purchase #3 $54.52   6.590%   $58.1129   $58.11   $58.10   $58.10  
  Purchase #4 $13.36   7.585%   $14.3734   $14.37   $14.35   $14.40  
  Purchase #5 $185.41   9.129%   $202.3361   $202.34   $202.35   $202.30  
  Purchase #6 $62.69   8.829%   $68.2249   $68.22   $68.20   $68.20  
  Purchase #7 $18.32   3.592%   $18.9781   $18.98   $19.00   $19.00  
  7 purchase totals = $705.33       $765.3033   $765.30   $765.30   $765.30