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 $248.60   7.474%   $267.1804   $267.18   $267.20   $267.20  
  Purchase #2 $16.89   5.634%   $17.8416   $17.84   $17.85   $17.80  
  Purchase #3 $169.44   9.539%   $185.6029   $185.60   $185.60   $185.60  
  Purchase #4 $170.49   4.579%   $178.2967   $178.30   $178.30   $178.30  
  Purchase #5 $87.56   8.857%   $95.3152   $95.32   $95.30   $95.30  
  Purchase #6 $34.37   7.827%   $37.0601   $37.06   $37.05   $37.10  
  Purchase #7 $241.76   10.583%   $267.3455   $267.35   $267.35   $267.30  
  7 purchase totals = $969.11       $1,048.6424   $1,048.65   $1,048.65   $1,048.60