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 $247.59   12.284%   $278.004   $278.00   $278.00   $278.00  
  Purchase #2 $13.94   6.358%   $14.8263   $14.83   $14.85   $14.80  
  Purchase #3 $215.39   6.846%   $230.1356   $230.14   $230.15   $230.10  
  Purchase #4 $171.30   6.673%   $182.7308   $182.73   $182.75   $182.70  
  Purchase #5 $72.67   10.641%   $80.4028   $80.40   $80.40   $80.40  
  Purchase #6 $219.85   5.479%   $231.8956   $231.90   $231.90   $231.90  
  Purchase #7 $164.67   5.644%   $173.964   $173.96   $173.95   $174.00  
  7 purchase totals = $1,105.41       $1,191.9591   $1,191.96   $1,192.00   $1,191.90