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 $79.31   5.810%   $83.9179   $83.92   $83.90   $83.90  
  Purchase #2 $178.90   8.408%   $193.9419   $193.94   $193.95   $193.90  
  Purchase #3 $227.32   8.174%   $245.9011   $245.90   $245.90   $245.90  
  Purchase #4 $92.88   6.449%   $98.8698   $98.87   $98.85   $98.90  
  Purchase #5 $58.91   3.838%   $61.171   $61.17   $61.15   $61.20  
  Purchase #6 $87.69   11.168%   $97.4832   $97.48   $97.50   $97.50  
  Purchase #7 $172.43   10.401%   $190.3644   $190.36   $190.35   $190.40  
  7 purchase totals = $897.44       $971.6493   $971.64   $971.60   $971.70