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 $232.56   8.377%   $252.0416   $252.04   $252.05   $252.00  
  Purchase #2 $203.42   7.118%   $217.8994   $217.90   $217.90   $217.90  
  Purchase #3 $132.32   5.582%   $139.7061   $139.71   $139.70   $139.70  
  Purchase #4 $215.44   9.213%   $235.2885   $235.29   $235.30   $235.30  
  Purchase #5 $158.27   3.435%   $163.7066   $163.71   $163.70   $163.70  
  Purchase #6 $22.61   3.367%   $23.3713   $23.37   $23.35   $23.40  
  Purchase #7 $31.57   12.272%   $35.4443   $35.44   $35.45   $35.40  
  7 purchase totals = $996.19       $1,067.4578   $1,067.46   $1,067.45   $1,067.40