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 $91.31   5.816%   $96.6206   $96.62   $96.60   $96.60  
  Purchase #2 $243.61   6.441%   $259.3009   $259.30   $259.30   $259.30  
  Purchase #3 $85.73   7.521%   $92.1778   $92.18   $92.20   $92.20  
  Purchase #4 $175.85   13.431%   $199.4684   $199.47   $199.45   $199.50  
  Purchase #5 $123.53   8.379%   $133.8806   $133.88   $133.90   $133.90  
  Purchase #6 $117.29   7.102%   $125.6199   $125.62   $125.60   $125.60  
  Purchase #7 $188.92   8.374%   $204.7402   $204.74   $204.75   $204.70  
  7 purchase totals = $1,026.24       $1,111.8084   $1,111.81   $1,111.80   $1,111.80