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 $30.48   6.115%   $32.3439   $32.34   $32.35   $32.30  
  Purchase #2 $106.67   10.709%   $118.0933   $118.09   $118.10   $118.10  
  Purchase #3 $158.34   4.754%   $165.8675   $165.87   $165.85   $165.90  
  Purchase #4 $198.77   11.173%   $220.9786   $220.98   $221.00   $221.00  
  Purchase #5 $250.86   6.642%   $267.5221   $267.52   $267.50   $267.50  
  Purchase #6 $95.54   5.710%   $100.9953   $101.00   $101.00   $101.00  
  Purchase #7 $14.78   9.642%   $16.2051   $16.21   $16.20   $16.20  
  7 purchase totals = $855.44       $922.0058   $922.01   $922.00   $922.00