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 $10.94   6.719%   $11.6751   $11.68   $11.70   $11.70  
  Purchase #2 $37.93   8.533%   $41.1666   $41.17   $41.15   $41.20  
  Purchase #3 $168.59   13.448%   $191.262   $191.26   $191.25   $191.30  
  Purchase #4 $58.66   5.357%   $61.8024   $61.80   $61.80   $61.80  
  Purchase #5 $238.41   12.338%   $267.825   $267.83   $267.85   $267.80  
  Purchase #6 $171.63   5.540%   $181.1383   $181.14   $181.15   $181.10  
  Purchase #7 $71.88   11.641%   $80.2476   $80.25   $80.25   $80.20  
  7 purchase totals = $758.04       $835.1170   $835.13   $835.15   $835.10