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 $29.74   12.763%   $33.5357   $33.54   $33.55   $33.50  
  Purchase #2 $92.46   6.164%   $98.1592   $98.16   $98.15   $98.20  
  Purchase #3 $75.92   7.273%   $81.4417   $81.44   $81.45   $81.40  
  Purchase #4 $68.73   7.535%   $73.9088   $73.91   $73.90   $73.90  
  Purchase #5 $168.81   13.607%   $191.78   $191.78   $191.80   $191.80  
  Purchase #6 $203.81   7.663%   $219.428   $219.43   $219.45   $219.40  
  Purchase #7 $72.70   6.211%   $77.2154   $77.22   $77.20   $77.20  
  7 purchase totals = $712.17       $775.4688   $775.48   $775.50   $775.40