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 $94.68   13.621%   $107.5764   $107.58   $107.60   $107.60  
  Purchase #2 $191.37   10.524%   $211.5098   $211.51   $211.50   $211.50  
  Purchase #3 $215.38   13.181%   $243.7692   $243.77   $243.75   $243.80  
  Purchase #4 $30.76   10.653%   $34.0369   $34.04   $34.05   $34.00  
  Purchase #5 $210.58   5.448%   $222.0524   $222.05   $222.05   $222.10  
  Purchase #6 $238.96   8.644%   $259.6157   $259.62   $259.60   $259.60  
  Purchase #7 $5.57   10.288%   $6.143   $6.14   $6.15   $6.10  
  7 purchase totals = $987.30       $1,084.7034   $1,084.71   $1,084.70   $1,084.70