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 $111.34   13.231%   $126.0714   $126.07   $126.05   $126.10  
  Purchase #2 $181.68   12.855%   $205.035   $205.04   $205.05   $205.00  
  Purchase #3 $89.65   4.353%   $93.5525   $93.55   $93.55   $93.60  
  Purchase #4 $119.43   9.856%   $131.201   $131.20   $131.20   $131.20  
  Purchase #5 $226.99   11.344%   $252.7397   $252.74   $252.75   $252.70  
  Purchase #6 $126.74   3.721%   $131.456   $131.46   $131.45   $131.50  
  Purchase #7 $12.57   6.626%   $13.4029   $13.40   $13.40   $13.40  
  7 purchase totals = $868.40       $953.4585   $953.46   $953.45   $953.50