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 $12.50   3.787%   $12.9734   $12.97   $12.95   $13.00  
  Purchase #2 $5.29   3.836%   $5.4929   $5.49   $5.50   $5.50  
  Purchase #3 $46.53   9.357%   $50.8838   $50.88   $50.90   $50.90  
  Purchase #4 $143.60   6.432%   $152.8364   $152.84   $152.85   $152.80  
  Purchase #5 $153.98   11.469%   $171.64   $171.64   $171.65   $171.60  
  Purchase #6 $240.61   7.622%   $258.9493   $258.95   $258.95   $258.90  
  Purchase #7 $90.99   10.205%   $100.2755   $100.28   $100.30   $100.30  
  7 purchase totals = $693.50       $753.0513   $753.05   $753.10   $753.00