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 $162.34   11.831%   $181.5464   $181.55   $181.55   $181.50  
  Purchase #2 $93.34   8.498%   $101.272   $101.27   $101.25   $101.30  
  Purchase #3 $23.94   11.866%   $26.7807   $26.78   $26.80   $26.80  
  Purchase #4 $220.28   7.372%   $236.519   $236.52   $236.50   $236.50  
  Purchase #5 $19.46   7.134%   $20.8483   $20.85   $20.85   $20.80  
  Purchase #6 $198.92   3.859%   $206.5963   $206.60   $206.60   $206.60  
  Purchase #7 $203.37   5.632%   $214.8238   $214.82   $214.80   $214.80  
  7 purchase totals = $921.65       $988.3865   $988.39   $988.35   $988.30