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 $149.93   8.431%   $162.5706   $162.57   $162.55   $162.60  
  Purchase #2 $248.99   4.755%   $260.8295   $260.83   $260.85   $260.80  
  Purchase #3 $17.86   5.354%   $18.8162   $18.82   $18.80   $18.80  
  Purchase #4 $242.52   12.300%   $272.35   $272.35   $272.35   $272.40  
  Purchase #5 $43.78   6.410%   $46.5863   $46.59   $46.60   $46.60  
  Purchase #6 $180.84   10.226%   $199.3327   $199.33   $199.35   $199.30  
  Purchase #7 $41.99   8.368%   $45.5037   $45.50   $45.50   $45.50  
  7 purchase totals = $925.91       $1,005.9890   $1,005.99   $1,006.00   $1,006.00