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 $118.93   4.747%   $124.5756   $124.58   $124.60   $124.60  
  Purchase #2 $223.60   11.269%   $248.7975   $248.80   $248.80   $248.80  
  Purchase #3 $31.27   11.187%   $34.7682   $34.77   $34.75   $34.80  
  Purchase #4 $150.31   8.214%   $162.6565   $162.66   $162.65   $162.70  
  Purchase #5 $173.32   5.639%   $183.0935   $183.09   $183.10   $183.10  
  Purchase #6 $60.99   10.474%   $67.3781   $67.38   $67.40   $67.40  
  Purchase #7 $244.68   5.741%   $258.7271   $258.73   $258.75   $258.70  
  7 purchase totals = $1,003.10       $1,079.9965   $1,080.01   $1,080.05   $1,080.10