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 $188.95   13.808%   $215.0402   $215.04   $215.05   $215.00  
  Purchase #2 $11.52   10.197%   $12.6947   $12.69   $12.70   $12.70  
  Purchase #3 $90.64   12.419%   $101.8966   $101.90   $101.90   $101.90  
  Purchase #4 $184.81   4.759%   $193.6051   $193.61   $193.60   $193.60  
  Purchase #5 $85.40   12.783%   $96.3167   $96.32   $96.30   $96.30  
  Purchase #6 $98.56   7.651%   $106.1008   $106.10   $106.10   $106.10  
  Purchase #7 $216.73   11.731%   $242.1546   $242.15   $242.15   $242.20  
  7 purchase totals = $876.61       $967.8087   $967.81   $967.80   $967.80