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 $244.37   5.848%   $258.6608   $258.66   $258.65   $258.70  
  Purchase #2 $59.34   4.742%   $62.1539   $62.15   $62.15   $62.20  
  Purchase #3 $170.91   12.194%   $191.7508   $191.75   $191.75   $191.80  
  Purchase #4 $195.94   9.624%   $214.7973   $214.80   $214.80   $214.80  
  Purchase #5 $52.58   6.698%   $56.1018   $56.10   $56.10   $56.10  
  Purchase #6 $248.66   10.342%   $274.3764   $274.38   $274.40   $274.40  
  Purchase #7 $207.72   5.435%   $219.0096   $219.01   $219.00   $219.00  
  7 purchase totals = $1,179.52       $1,276.8506   $1,276.85   $1,276.85   $1,277.00