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 $179.56   7.497%   $193.0216   $193.02   $193.00   $193.00  
  Purchase #2 $119.66   12.316%   $134.3973   $134.40   $134.40   $134.40  
  Purchase #3 $52.60   7.776%   $56.6902   $56.69   $56.70   $56.70  
  Purchase #4 $16.69   11.227%   $18.5638   $18.56   $18.55   $18.60  
  Purchase #5 $193.63   3.591%   $200.5833   $200.58   $200.60   $200.60  
  Purchase #6 $23.92   4.599%   $25.0201   $25.02   $25.00   $25.00  
  Purchase #7 $210.36   11.147%   $233.8088   $233.81   $233.80   $233.80  
  7 purchase totals = $796.42       $862.0851   $862.08   $862.05   $862.10