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 $14.85   13.794%   $16.8984   $16.90   $16.90   $16.90  
  Purchase #2 $161.76   12.305%   $181.6646   $181.66   $181.65   $181.70  
  Purchase #3 $34.93   5.845%   $36.9717   $36.97   $36.95   $37.00  
  Purchase #4 $244.75   4.144%   $254.8924   $254.89   $254.90   $254.90  
  Purchase #5 $121.63   10.537%   $134.4462   $134.45   $134.45   $134.40  
  Purchase #6 $169.87   10.731%   $188.0987   $188.10   $188.10   $188.10  
  Purchase #7 $146.98   6.195%   $156.0854   $156.09   $156.10   $156.10  
  7 purchase totals = $894.77       $969.0574   $969.06   $969.05   $969.10