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 $191.27   5.782%   $202.3292   $202.33   $202.35   $202.30  
  Purchase #2 $23.84   7.812%   $25.7024   $25.70   $25.70   $25.70  
  Purchase #3 $235.61   10.365%   $260.031   $260.03   $260.05   $260.00  
  Purchase #4 $244.27   7.550%   $262.7124   $262.71   $262.70   $262.70  
  Purchase #5 $65.80   5.313%   $69.296   $69.30   $69.30   $69.30  
  Purchase #6 $131.27   8.186%   $142.0158   $142.02   $142.00   $142.00  
  Purchase #7 $159.66   11.195%   $177.5339   $177.53   $177.55   $177.50  
  7 purchase totals = $1,051.72       $1,139.6207   $1,139.62   $1,139.65   $1,139.50