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 $84.30   13.766%   $95.9047   $95.90   $95.90   $95.90  
  Purchase #2 $52.86   7.542%   $56.8467   $56.85   $56.85   $56.80  
  Purchase #3 $108.92   7.601%   $117.199   $117.20   $117.20   $117.20  
  Purchase #4 $140.49   7.624%   $151.201   $151.20   $151.20   $151.20  
  Purchase #5 $57.98   11.821%   $64.8338   $64.83   $64.85   $64.80  
  Purchase #6 $9.55   10.488%   $10.5516   $10.55   $10.55   $10.60  
  Purchase #7 $167.95   7.776%   $181.0098   $181.01   $181.00   $181.00  
  7 purchase totals = $622.05       $677.5466   $677.54   $677.55   $677.50