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 $38.67   12.709%   $43.5846   $43.58   $43.60   $43.60  
  Purchase #2 $168.85   10.863%   $187.1922   $187.19   $187.20   $187.20  
  Purchase #3 $162.40   7.207%   $174.1042   $174.10   $174.10   $174.10  
  Purchase #4 $137.47   6.710%   $146.6942   $146.69   $146.70   $146.70  
  Purchase #5 $172.60   10.626%   $190.9405   $190.94   $190.95   $190.90  
  Purchase #6 $249.71   6.753%   $266.5729   $266.57   $266.55   $266.60  
  Purchase #7 $10.54   11.458%   $11.7477   $11.75   $11.75   $11.70  
  7 purchase totals = $940.24       $1,020.8363   $1,020.82   $1,020.85   $1,020.80