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 $241.77   9.454%   $264.6269   $264.63   $264.65   $264.60  
  Purchase #2 $212.26   3.472%   $219.6297   $219.63   $219.65   $219.60  
  Purchase #3 $125.52   9.603%   $137.5737   $137.57   $137.55   $137.60  
  Purchase #4 $198.79   10.509%   $219.6808   $219.68   $219.70   $219.70  
  Purchase #5 $234.48   4.166%   $244.2484   $244.25   $244.25   $244.20  
  Purchase #6 $231.69   8.673%   $251.7845   $251.78   $251.80   $251.80  
  Purchase #7 $81.53   6.582%   $86.8963   $86.90   $86.90   $86.90  
  7 purchase totals = $1,326.04       $1,424.4403   $1,424.44   $1,424.50   $1,424.40