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 $29.95   10.701%   $33.1549   $33.15   $33.15   $33.20  
  Purchase #2 $57.53   4.375%   $60.0469   $60.05   $60.05   $60.00  
  Purchase #3 $130.51   12.712%   $147.1004   $147.10   $147.10   $147.10  
  Purchase #4 $75.50   3.690%   $78.286   $78.29   $78.30   $78.30  
  Purchase #5 $146.53   7.605%   $157.6736   $157.67   $157.65   $157.70  
  Purchase #6 $180.35   13.578%   $204.8379   $204.84   $204.85   $204.80  
  Purchase #7 $33.73   12.644%   $37.9948   $37.99   $38.00   $38.00  
  7 purchase totals = $654.10       $719.0945   $719.09   $719.10   $719.10