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 $188.85   8.521%   $204.9419   $204.94   $204.95   $204.90  
  Purchase #2 $154.43   13.820%   $175.7722   $175.77   $175.75   $175.80  
  Purchase #3 $127.72   8.153%   $138.133   $138.13   $138.15   $138.10  
  Purchase #4 $69.87   4.149%   $72.7689   $72.77   $72.75   $72.80  
  Purchase #5 $212.89   4.206%   $221.8442   $221.84   $221.85   $221.80  
  Purchase #6 $86.86   9.396%   $95.0214   $95.02   $95.00   $95.00  
  Purchase #7 $52.95   8.215%   $57.2998   $57.30   $57.30   $57.30  
  7 purchase totals = $893.57       $965.7814   $965.77   $965.75   $965.70