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 $140.29   3.622%   $145.3713   $145.37   $145.35   $145.40  
  Purchase #2 $221.56   5.612%   $233.9939   $233.99   $234.00   $234.00  
  Purchase #3 $232.47   7.675%   $250.3121   $250.31   $250.30   $250.30  
  Purchase #4 $221.37   10.310%   $244.1932   $244.19   $244.20   $244.20  
  Purchase #5 $225.72   10.220%   $248.7886   $248.79   $248.80   $248.80  
  Purchase #6 $230.31   3.719%   $238.8752   $238.88   $238.90   $238.90  
  Purchase #7 $161.42   10.804%   $178.8598   $178.86   $178.85   $178.90  
  7 purchase totals = $1,433.14       $1,540.3941   $1,540.39   $1,540.40   $1,540.50