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 $216.51   11.456%   $241.3134   $241.31   $241.30   $241.30  
  Purchase #2 $152.57   3.392%   $157.7452   $157.75   $157.75   $157.70  
  Purchase #3 $26.25   3.643%   $27.2063   $27.21   $27.20   $27.20  
  Purchase #4 $167.54   9.106%   $182.7962   $182.80   $182.80   $182.80  
  Purchase #5 $97.49   10.798%   $108.017   $108.02   $108.00   $108.00  
  Purchase #6 $208.64   8.146%   $225.6358   $225.64   $225.65   $225.60  
  Purchase #7 $59.87   3.387%   $61.8978   $61.90   $61.90   $61.90  
  7 purchase totals = $928.87       $1,004.6117   $1,004.63   $1,004.60   $1,004.50