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 $185.97   11.485%   $207.3287   $207.33   $207.35   $207.30  
  Purchase #2 $187.27   11.189%   $208.2236   $208.22   $208.20   $208.20  
  Purchase #3 $237.55   12.643%   $267.5834   $267.58   $267.60   $267.60  
  Purchase #4 $191.89   4.686%   $200.882   $200.88   $200.90   $200.90  
  Purchase #5 $236.90   4.199%   $246.8474   $246.85   $246.85   $246.80  
  Purchase #6 $202.73   11.537%   $226.119   $226.12   $226.10   $226.10  
  Purchase #7 $178.52   8.273%   $193.289   $193.29   $193.30   $193.30  
  7 purchase totals = $1,420.83       $1,550.2731   $1,550.27   $1,550.30   $1,550.20