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 $184.87   10.156%   $203.6454   $203.65   $203.65   $203.60  
  Purchase #2 $190.77   12.740%   $215.0741   $215.07   $215.05   $215.10  
  Purchase #3 $213.87   13.443%   $242.6205   $242.62   $242.60   $242.60  
  Purchase #4 $224.63   8.451%   $243.6135   $243.61   $243.60   $243.60  
  Purchase #5 $187.45   9.797%   $205.8145   $205.81   $205.80   $205.80  
  Purchase #6 $78.45   6.852%   $83.8254   $83.83   $83.85   $83.80  
  Purchase #7 $41.69   9.405%   $45.6109   $45.61   $45.60   $45.60  
  7 purchase totals = $1,121.73       $1,240.2043   $1,240.20   $1,240.15   $1,240.10