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 $235.68   3.368%   $243.6177   $243.62   $243.60   $243.60  
  Purchase #2 $51.74   8.867%   $56.3278   $56.33   $56.35   $56.30  
  Purchase #3 $233.49   6.781%   $249.323   $249.32   $249.30   $249.30  
  Purchase #4 $24.81   7.396%   $26.6449   $26.64   $26.65   $26.60  
  Purchase #5 $66.33   7.502%   $71.3061   $71.31   $71.30   $71.30  
  Purchase #6 $194.52   7.180%   $208.4865   $208.49   $208.50   $208.50  
  Purchase #7 $208.71   4.273%   $217.6282   $217.63   $217.65   $217.60  
  7 purchase totals = $1,015.28       $1,073.3342   $1,073.34   $1,073.35   $1,073.20