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 $68.81   12.867%   $77.6638   $77.66   $77.65   $77.70  
  Purchase #2 $99.46   5.107%   $104.5394   $104.54   $104.55   $104.50  
  Purchase #3 $25.86   3.743%   $26.8279   $26.83   $26.85   $26.80  
  Purchase #4 $152.97   3.400%   $158.171   $158.17   $158.15   $158.20  
  Purchase #5 $118.44   5.408%   $124.8452   $124.85   $124.85   $124.80  
  Purchase #6 $182.51   13.450%   $207.0576   $207.06   $207.05   $207.10  
  Purchase #7 $234.93   13.253%   $266.0653   $266.07   $266.05   $266.10  
  7 purchase totals = $882.98       $965.1702   $965.18   $965.15   $965.20