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 $67.64   12.207%   $75.8968   $75.90   $75.90   $75.90  
  Purchase #2 $95.33   12.322%   $107.0766   $107.08   $107.10   $107.10  
  Purchase #3 $54.43   11.329%   $60.5964   $60.60   $60.60   $60.60  
  Purchase #4 $123.36   9.137%   $134.6314   $134.63   $134.65   $134.60  
  Purchase #5 $144.77   7.861%   $156.1504   $156.15   $156.15   $156.20  
  Purchase #6 $184.97   8.619%   $200.9126   $200.91   $200.90   $200.90  
  Purchase #7 $192.64   4.177%   $200.6866   $200.69   $200.70   $200.70  
  7 purchase totals = $863.14       $935.9508   $935.96   $936.00   $936.00