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 $119.84   12.529%   $134.8548   $134.85   $134.85   $134.90  
  Purchase #2 $65.30   6.543%   $69.5726   $69.57   $69.55   $69.60  
  Purchase #3 $47.65   13.757%   $54.2052   $54.21   $54.20   $54.20  
  Purchase #4 $127.74   6.276%   $135.757   $135.76   $135.75   $135.80  
  Purchase #5 $235.80   11.586%   $263.1198   $263.12   $263.10   $263.10  
  Purchase #6 $125.84   10.499%   $139.0519   $139.05   $139.05   $139.10  
  Purchase #7 $79.54   7.757%   $85.7099   $85.71   $85.70   $85.70  
  7 purchase totals = $801.71       $882.2712   $882.27   $882.20   $882.40