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 $153.43   8.803%   $166.9364   $166.94   $166.95   $166.90  
  Purchase #2 $52.34   8.311%   $56.69   $56.69   $56.70   $56.70  
  Purchase #3 $186.54   7.216%   $200.0007   $200.00   $200.00   $200.00  
  Purchase #4 $242.72   6.660%   $258.8852   $258.89   $258.90   $258.90  
  Purchase #5 $86.54   8.365%   $93.7791   $93.78   $93.80   $93.80  
  Purchase #6 $26.77   5.440%   $28.2263   $28.23   $28.25   $28.20  
  Purchase #7 $53.79   5.518%   $56.7581   $56.76   $56.75   $56.80  
  7 purchase totals = $802.13       $861.2758   $861.29   $861.35   $861.30