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 $228.71   10.619%   $252.9967   $253.00   $253.00   $253.00  
  Purchase #2 $197.90   12.699%   $223.0313   $223.03   $223.05   $223.00  
  Purchase #3 $118.85   5.521%   $125.4117   $125.41   $125.40   $125.40  
  Purchase #4 $131.42   11.295%   $146.2639   $146.26   $146.25   $146.30  
  Purchase #5 $23.30   10.795%   $25.8152   $25.82   $25.80   $25.80  
  Purchase #6 $38.87   6.209%   $41.2834   $41.28   $41.30   $41.30  
  Purchase #7 $243.91   4.227%   $254.2201   $254.22   $254.20   $254.20  
  7 purchase totals = $982.96       $1,069.0223   $1,069.02   $1,069.00   $1,069.00