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 $248.85   5.596%   $262.7756   $262.78   $262.80   $262.80  
  Purchase #2 $159.57   13.154%   $180.5598   $180.56   $180.55   $180.60  
  Purchase #3 $105.50   13.481%   $119.7225   $119.72   $119.70   $119.70  
  Purchase #4 $171.80   12.796%   $193.7835   $193.78   $193.80   $193.80  
  Purchase #5 $184.63   13.768%   $210.0499   $210.05   $210.05   $210.00  
  Purchase #6 $204.97   4.204%   $213.5869   $213.59   $213.60   $213.60  
  Purchase #7 $83.33   5.503%   $87.9156   $87.92   $87.90   $87.90  
  7 purchase totals = $1,158.65       $1,268.3938   $1,268.40   $1,268.40   $1,268.40