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 $38.82   10.361%   $42.8421   $42.84   $42.85   $42.80  
  Purchase #2 $53.67   12.410%   $60.3304   $60.33   $60.35   $60.30  
  Purchase #3 $170.44   7.462%   $183.1582   $183.16   $183.15   $183.20  
  Purchase #4 $224.40   9.383%   $245.4555   $245.46   $245.45   $245.50  
  Purchase #5 $181.66   12.688%   $204.709   $204.71   $204.70   $204.70  
  Purchase #6 $212.87   6.826%   $227.4005   $227.40   $227.40   $227.40  
  Purchase #7 $82.42   11.202%   $91.6527   $91.65   $91.65   $91.70  
  7 purchase totals = $964.28       $1,055.5484   $1,055.55   $1,055.55   $1,055.60