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 $239.27   6.295%   $254.332   $254.33   $254.35   $254.30  
  Purchase #2 $232.55   6.350%   $247.3169   $247.32   $247.30   $247.30  
  Purchase #3 $148.28   9.230%   $161.9662   $161.97   $161.95   $162.00  
  Purchase #4 $57.63   8.587%   $62.5787   $62.58   $62.60   $62.60  
  Purchase #5 $214.50   11.569%   $239.3155   $239.32   $239.30   $239.30  
  Purchase #6 $35.95   3.765%   $37.3035   $37.30   $37.30   $37.30  
  Purchase #7 $23.35   8.807%   $25.4064   $25.41   $25.40   $25.40  
  7 purchase totals = $951.53       $1,028.2192   $1,028.23   $1,028.20   $1,028.20