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 $93.26   11.722%   $104.1919   $104.19   $104.20   $104.20  
  Purchase #2 $31.25   9.277%   $34.1491   $34.15   $34.15   $34.10  
  Purchase #3 $225.73   6.691%   $240.8336   $240.83   $240.85   $240.80  
  Purchase #4 $98.42   12.170%   $110.3977   $110.40   $110.40   $110.40  
  Purchase #5 $135.53   6.725%   $144.6444   $144.64   $144.65   $144.60  
  Purchase #6 $211.77   3.238%   $218.6271   $218.63   $218.65   $218.60  
  Purchase #7 $187.67   13.237%   $212.5119   $212.51   $212.50   $212.50  
  7 purchase totals = $983.63       $1,065.3557   $1,065.35   $1,065.40   $1,065.20