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 $93.49   3.138%   $96.4237   $96.42   $96.40   $96.40  
  Purchase #2 $246.86   11.474%   $275.1847   $275.18   $275.20   $275.20  
  Purchase #3 $18.84   4.226%   $19.6362   $19.64   $19.65   $19.60  
  Purchase #4 $212.77   4.282%   $221.8808   $221.88   $221.90   $221.90  
  Purchase #5 $180.25   3.316%   $186.2271   $186.23   $186.25   $186.20  
  Purchase #6 $217.96   11.860%   $243.8101   $243.81   $243.80   $243.80  
  Purchase #7 $157.84   12.252%   $177.1786   $177.18   $177.20   $177.20  
  7 purchase totals = $1,128.01       $1,220.3412   $1,220.34   $1,220.40   $1,220.30