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 $246.67   8.648%   $268.002   $268.00   $268.00   $268.00  
  Purchase #2 $114.43   6.587%   $121.9675   $121.97   $121.95   $122.00  
  Purchase #3 $243.36   4.480%   $254.2625   $254.26   $254.25   $254.30  
  Purchase #4 $191.41   11.201%   $212.8498   $212.85   $212.85   $212.80  
  Purchase #5 $248.37   4.549%   $259.6684   $259.67   $259.65   $259.70  
  Purchase #6 $231.70   13.648%   $263.3224   $263.32   $263.30   $263.30  
  Purchase #7 $49.93   3.529%   $51.692   $51.69   $51.70   $51.70  
  7 purchase totals = $1,325.87       $1,431.7646   $1,431.76   $1,431.70   $1,431.80