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 $158.91   11.543%   $177.253   $177.25   $177.25   $177.30  
  Purchase #2 $6.84   5.689%   $7.2291   $7.23   $7.25   $7.20  
  Purchase #3 $85.62   3.504%   $88.6201   $88.62   $88.60   $88.60  
  Purchase #4 $37.88   13.720%   $43.0771   $43.08   $43.10   $43.10  
  Purchase #5 $45.37   10.820%   $50.279   $50.28   $50.30   $50.30  
  Purchase #6 $118.69   5.464%   $125.1752   $125.18   $125.20   $125.20  
  Purchase #7 $78.63   7.694%   $84.6798   $84.68   $84.70   $84.70  
  7 purchase totals = $531.94       $576.3133   $576.32   $576.40   $576.40