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 $58.99   5.399%   $62.1749   $62.17   $62.15   $62.20  
  Purchase #2 $74.36   7.408%   $79.8686   $79.87   $79.85   $79.90  
  Purchase #3 $62.36   3.784%   $64.7197   $64.72   $64.70   $64.70  
  Purchase #4 $214.37   11.115%   $238.1972   $238.20   $238.20   $238.20  
  Purchase #5 $188.70   3.279%   $194.8875   $194.89   $194.90   $194.90  
  Purchase #6 $204.34   12.350%   $229.576   $229.58   $229.60   $229.60  
  Purchase #7 $36.25   6.743%   $38.6943   $38.69   $38.70   $38.70  
  7 purchase totals = $839.37       $908.1182   $908.12   $908.10   $908.20