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 $50.66   7.771%   $54.5968   $54.60   $54.60   $54.60  
  Purchase #2 $58.25   5.438%   $61.4176   $61.42   $61.40   $61.40  
  Purchase #3 $219.89   12.696%   $247.8072   $247.81   $247.80   $247.80  
  Purchase #4 $121.52   10.833%   $134.6843   $134.68   $134.70   $134.70  
  Purchase #5 $68.95   8.765%   $74.9935   $74.99   $75.00   $75.00  
  Purchase #6 $205.81   4.200%   $214.454   $214.45   $214.45   $214.50  
  Purchase #7 $10.46   12.127%   $11.7285   $11.73   $11.75   $11.70  
  7 purchase totals = $735.54       $799.6819   $799.68   $799.70   $799.70