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 $104.49   13.422%   $118.5146   $118.51   $118.50   $118.50  
  Purchase #2 $194.66   3.870%   $202.1933   $202.19   $202.20   $202.20  
  Purchase #3 $92.29   13.514%   $104.7621   $104.76   $104.75   $104.80  
  Purchase #4 $123.32   13.259%   $139.671   $139.67   $139.65   $139.70  
  Purchase #5 $203.84   9.643%   $223.4963   $223.50   $223.50   $223.50  
  Purchase #6 $12.44   9.565%   $13.6299   $13.63   $13.65   $13.60  
  Purchase #7 $246.32   10.746%   $272.7895   $272.79   $272.80   $272.80  
  7 purchase totals = $977.36       $1,075.0567   $1,075.05   $1,075.05   $1,075.10