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 $103.91   5.186%   $109.2988   $109.30   $109.30   $109.30  
  Purchase #2 $234.72   8.192%   $253.9483   $253.95   $253.95   $253.90  
  Purchase #3 $20.69   4.854%   $21.6943   $21.69   $21.70   $21.70  
  Purchase #4 $54.67   9.703%   $59.9746   $59.97   $59.95   $60.00  
  Purchase #5 $244.98   4.820%   $256.788   $256.79   $256.80   $256.80  
  Purchase #6 $55.42   13.746%   $63.038   $63.04   $63.05   $63.00  
  Purchase #7 $171.97   13.557%   $195.284   $195.28   $195.30   $195.30  
  7 purchase totals = $886.36       $960.0260   $960.02   $960.05   $960.00