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 $113.96   3.523%   $117.9748   $117.97   $117.95   $118.00  
  Purchase #2 $179.55   7.694%   $193.3646   $193.36   $193.35   $193.40  
  Purchase #3 $16.45   13.462%   $18.6645   $18.66   $18.65   $18.70  
  Purchase #4 $146.79   13.295%   $166.3057   $166.31   $166.30   $166.30  
  Purchase #5 $125.88   3.182%   $129.8855   $129.89   $129.90   $129.90  
  Purchase #6 $142.70   5.826%   $151.0137   $151.01   $151.00   $151.00  
  Purchase #7 $44.99   10.783%   $49.8413   $49.84   $49.85   $49.80  
  7 purchase totals = $770.32       $827.0501   $827.04   $827.00   $827.10