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 $61.42   11.596%   $68.5423   $68.54   $68.55   $68.50  
  Purchase #2 $148.59   9.163%   $162.2053   $162.21   $162.20   $162.20  
  Purchase #3 $128.42   12.680%   $144.7037   $144.70   $144.70   $144.70  
  Purchase #4 $72.98   9.141%   $79.6511   $79.65   $79.65   $79.70  
  Purchase #5 $149.43   9.625%   $163.8126   $163.81   $163.80   $163.80  
  Purchase #6 $154.55   12.247%   $173.4777   $173.48   $173.50   $173.50  
  Purchase #7 $84.37   12.207%   $94.669   $94.67   $94.65   $94.70  
  7 purchase totals = $799.76       $887.0617   $887.06   $887.05   $887.10