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 $13.54   5.852%   $14.3324   $14.33   $14.35   $14.30  
  Purchase #2 $100.85   4.389%   $105.2763   $105.28   $105.30   $105.30  
  Purchase #3 $112.98   3.546%   $116.9863   $116.99   $117.00   $117.00  
  Purchase #4 $99.50   7.334%   $106.7973   $106.80   $106.80   $106.80  
  Purchase #5 $19.95   13.822%   $22.7075   $22.71   $22.70   $22.70  
  Purchase #6 $230.93   11.482%   $257.4454   $257.45   $257.45   $257.40  
  Purchase #7 $107.84   9.676%   $118.2746   $118.27   $118.25   $118.30  
  7 purchase totals = $685.59       $741.8198   $741.83   $741.85   $741.80