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 $222.27   6.423%   $236.5464   $236.55   $236.55   $236.50  
  Purchase #2 $115.54   7.283%   $123.9548   $123.95   $123.95   $124.00  
  Purchase #3 $56.98   9.584%   $62.441   $62.44   $62.45   $62.40  
  Purchase #4 $159.34   4.155%   $165.9606   $165.96   $165.95   $166.00  
  Purchase #5 $220.65   11.218%   $245.4025   $245.40   $245.40   $245.40  
  Purchase #6 $64.26   13.673%   $73.0463   $73.05   $73.05   $73.00  
  Purchase #7 $145.66   7.124%   $156.0368   $156.04   $156.05   $156.00  
  7 purchase totals = $984.70       $1,063.3884   $1,063.39   $1,063.40   $1,063.30