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 $233.72   13.463%   $265.1857   $265.19   $265.20   $265.20  
  Purchase #2 $58.29   3.643%   $60.4135   $60.41   $60.40   $60.40  
  Purchase #3 $185.29   3.690%   $192.1272   $192.13   $192.15   $192.10  
  Purchase #4 $247.85   8.155%   $268.0622   $268.06   $268.05   $268.10  
  Purchase #5 $231.57   3.157%   $238.8807   $238.88   $238.90   $238.90  
  Purchase #6 $208.68   11.609%   $232.9057   $232.91   $232.90   $232.90  
  Purchase #7 $24.39   8.648%   $26.4992   $26.50   $26.50   $26.50  
  7 purchase totals = $1,189.79       $1,284.0742   $1,284.08   $1,284.10   $1,284.10