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 $58.53   4.153%   $60.9608   $60.96   $60.95   $61.00  
  Purchase #2 $167.35   8.399%   $181.4057   $181.41   $181.40   $181.40  
  Purchase #3 $97.52   3.194%   $100.6348   $100.63   $100.65   $100.60  
  Purchase #4 $195.96   8.873%   $213.3475   $213.35   $213.35   $213.30  
  Purchase #5 $59.39   5.660%   $62.7515   $62.75   $62.75   $62.80  
  Purchase #6 $38.72   10.623%   $42.8332   $42.83   $42.85   $42.80  
  Purchase #7 $9.81   7.575%   $10.5531   $10.55   $10.55   $10.60  
  7 purchase totals = $627.28       $672.4866   $672.48   $672.50   $672.50