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 $77.57   9.642%   $85.0493   $85.05   $85.05   $85.00  
  Purchase #2 $176.76   7.869%   $190.6692   $190.67   $190.65   $190.70  
  Purchase #3 $146.88   11.737%   $164.1193   $164.12   $164.10   $164.10  
  Purchase #4 $218.59   12.207%   $245.2733   $245.27   $245.25   $245.30  
  Purchase #5 $195.73   7.647%   $210.6975   $210.70   $210.70   $210.70  
  Purchase #6 $81.39   4.169%   $84.7831   $84.78   $84.80   $84.80  
  Purchase #7 $163.93   7.272%   $175.851   $175.85   $175.85   $175.90  
  7 purchase totals = $1,060.85       $1,156.4427   $1,156.44   $1,156.40   $1,156.50