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 $201.87   6.102%   $214.1881   $214.19   $214.20   $214.20  
  Purchase #2 $21.96   9.730%   $24.0967   $24.10   $24.10   $24.10  
  Purchase #3 $92.75   3.122%   $95.6457   $95.65   $95.65   $95.60  
  Purchase #4 $219.64   6.817%   $234.6129   $234.61   $234.60   $234.60  
  Purchase #5 $37.26   5.815%   $39.4267   $39.43   $39.45   $39.40  
  Purchase #6 $134.33   6.168%   $142.6155   $142.62   $142.60   $142.60  
  Purchase #7 $233.71   8.154%   $252.7667   $252.77   $252.75   $252.80  
  7 purchase totals = $941.52       $1,003.3523   $1,003.37   $1,003.35   $1,003.30