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 $129.85   8.854%   $141.3469   $141.35   $141.35   $141.30  
  Purchase #2 $204.68   4.452%   $213.7924   $213.79   $213.80   $213.80  
  Purchase #3 $18.72   6.308%   $19.9009   $19.90   $19.90   $19.90  
  Purchase #4 $55.93   4.533%   $58.4653   $58.47   $58.45   $58.50  
  Purchase #5 $152.90   5.558%   $161.3982   $161.40   $161.40   $161.40  
  Purchase #6 $177.79   7.623%   $191.3429   $191.34   $191.35   $191.30  
  Purchase #7 $214.72   4.197%   $223.7318   $223.73   $223.75   $223.70  
  7 purchase totals = $954.59       $1,009.9784   $1,009.98   $1,010.00   $1,009.90