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 $208.25   8.780%   $226.5344   $226.53   $226.55   $226.50  
  Purchase #2 $215.47   13.127%   $243.7547   $243.75   $243.75   $243.80  
  Purchase #3 $24.59   7.269%   $26.3774   $26.38   $26.40   $26.40  
  Purchase #4 $185.90   6.503%   $197.9891   $197.99   $198.00   $198.00  
  Purchase #5 $177.45   5.505%   $187.2186   $187.22   $187.20   $187.20  
  Purchase #6 $45.73   5.643%   $48.3105   $48.31   $48.30   $48.30  
  Purchase #7 $135.33   13.200%   $153.1936   $153.19   $153.20   $153.20  
  7 purchase totals = $992.72       $1,083.3783   $1,083.37   $1,083.40   $1,083.40