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 $238.39   13.104%   $269.6286   $269.63   $269.65   $269.60  
  Purchase #2 $180.48   3.519%   $186.8311   $186.83   $186.85   $186.80  
  Purchase #3 $83.80   12.770%   $94.5013   $94.50   $94.50   $94.50  
  Purchase #4 $201.84   7.712%   $217.4059   $217.41   $217.40   $217.40  
  Purchase #5 $250.97   6.598%   $267.529   $267.53   $267.55   $267.50  
  Purchase #6 $201.75   10.670%   $223.2767   $223.28   $223.30   $223.30  
  Purchase #7 $59.73   13.593%   $67.8491   $67.85   $67.85   $67.80  
  7 purchase totals = $1,216.96       $1,327.0217   $1,327.03   $1,327.10   $1,326.90