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 $201.81   6.168%   $214.2576   $214.26   $214.25   $214.30  
  Purchase #2 $125.84   6.197%   $133.6383   $133.64   $133.65   $133.60  
  Purchase #3 $212.32   9.436%   $232.3545   $232.35   $232.35   $232.40  
  Purchase #4 $244.67   12.337%   $274.8549   $274.85   $274.85   $274.90  
  Purchase #5 $74.82   9.833%   $82.1771   $82.18   $82.20   $82.20  
  Purchase #6 $102.41   12.120%   $114.8221   $114.82   $114.80   $114.80  
  Purchase #7 $111.29   9.279%   $121.6166   $121.62   $121.60   $121.60  
  7 purchase totals = $1,073.16       $1,173.7211   $1,173.72   $1,173.70   $1,173.80