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 $99.87   13.174%   $113.0269   $113.03   $113.05   $113.00  
  Purchase #2 $242.34   4.695%   $253.7179   $253.72   $253.70   $253.70  
  Purchase #3 $48.67   5.772%   $51.4792   $51.48   $51.50   $51.50  
  Purchase #4 $119.30   4.325%   $124.4597   $124.46   $124.45   $124.50  
  Purchase #5 $162.69   5.780%   $172.0935   $172.09   $172.10   $172.10  
  Purchase #6 $88.35   7.863%   $95.297   $95.30   $95.30   $95.30  
  Purchase #7 $58.77   4.818%   $61.6015   $61.60   $61.60   $61.60  
  7 purchase totals = $819.99       $871.6757   $871.68   $871.70   $871.70