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 $60.77   8.580%   $65.9841   $65.98   $66.00   $66.00  
  Purchase #2 $238.32   10.378%   $263.0528   $263.05   $263.05   $263.10  
  Purchase #3 $18.47   11.617%   $20.6157   $20.62   $20.60   $20.60  
  Purchase #4 $192.79   4.169%   $200.8274   $200.83   $200.85   $200.80  
  Purchase #5 $7.70   13.696%   $8.7546   $8.75   $8.75   $8.80  
  Purchase #6 $100.73   6.529%   $107.3067   $107.31   $107.30   $107.30  
  Purchase #7 $175.99   10.669%   $194.7664   $194.77   $194.75   $194.80  
  7 purchase totals = $794.77       $861.3077   $861.31   $861.30   $861.40