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 $153.80   11.765%   $171.8946   $171.89   $171.90   $171.90  
  Purchase #2 $231.97   10.629%   $256.6261   $256.63   $256.65   $256.60  
  Purchase #3 $51.98   8.329%   $56.3094   $56.31   $56.30   $56.30  
  Purchase #4 $177.84   7.792%   $191.6973   $191.70   $191.70   $191.70  
  Purchase #5 $33.54   7.858%   $36.1756   $36.18   $36.20   $36.20  
  Purchase #6 $67.67   12.381%   $76.0482   $76.05   $76.05   $76.00  
  Purchase #7 $196.79   4.661%   $205.9624   $205.96   $205.95   $206.00  
  7 purchase totals = $913.59       $994.7136   $994.72   $994.75   $994.70