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 $235.56   8.654%   $255.9454   $255.95   $255.95   $255.90  
  Purchase #2 $119.92   5.298%   $126.2734   $126.27   $126.25   $126.30  
  Purchase #3 $184.46   5.419%   $194.4559   $194.46   $194.45   $194.50  
  Purchase #4 $25.63   8.831%   $27.8934   $27.89   $27.90   $27.90  
  Purchase #5 $198.64   10.653%   $219.8011   $219.80   $219.80   $219.80  
  Purchase #6 $243.45   3.661%   $252.3627   $252.36   $252.35   $252.40  
  Purchase #7 $158.29   13.529%   $179.7051   $179.71   $179.70   $179.70  
  7 purchase totals = $1,165.95       $1,256.4370   $1,256.44   $1,256.40   $1,256.50