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 $54.73   13.318%   $62.0189   $62.02   $62.00   $62.00  
  Purchase #2 $8.48   8.282%   $9.1823   $9.18   $9.20   $9.20  
  Purchase #3 $81.25   4.845%   $85.1866   $85.19   $85.20   $85.20  
  Purchase #4 $15.78   4.680%   $16.5185   $16.52   $16.50   $16.50  
  Purchase #5 $18.52   3.608%   $19.1882   $19.19   $19.20   $19.20  
  Purchase #6 $63.44   7.128%   $67.962   $67.96   $67.95   $68.00  
  Purchase #7 $36.59   6.821%   $39.0858   $39.09   $39.10   $39.10  
  7 purchase totals = $278.79       $299.1423   $299.15   $299.15   $299.20