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 $65.26   5.791%   $69.0392   $69.04   $69.05   $69.00  
  Purchase #2 $93.57   4.171%   $97.4728   $97.47   $97.45   $97.50  
  Purchase #3 $32.37   10.146%   $35.6543   $35.65   $35.65   $35.70  
  Purchase #4 $170.33   8.214%   $184.3209   $184.32   $184.30   $184.30  
  Purchase #5 $26.55   9.741%   $29.1362   $29.14   $29.15   $29.10  
  Purchase #6 $125.46   8.541%   $136.1755   $136.18   $136.20   $136.20  
  Purchase #7 $210.91   5.859%   $223.2672   $223.27   $223.25   $223.30  
  7 purchase totals = $724.45       $775.0661   $775.07   $775.05   $775.10