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 $210.69   6.709%   $224.8252   $224.83   $224.85   $224.80  
  Purchase #2 $219.94   8.798%   $239.2903   $239.29   $239.30   $239.30  
  Purchase #3 $7.88   5.623%   $8.3231   $8.32   $8.30   $8.30  
  Purchase #4 $236.41   7.551%   $254.2613   $254.26   $254.25   $254.30  
  Purchase #5 $105.58   4.856%   $110.707   $110.71   $110.70   $110.70  
  Purchase #6 $110.62   4.186%   $115.2506   $115.25   $115.25   $115.30  
  Purchase #7 $56.51   4.539%   $59.075   $59.08   $59.10   $59.10  
  7 purchase totals = $947.63       $1,011.7325   $1,011.74   $1,011.75   $1,011.80