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 $87.68   8.252%   $94.9154   $94.92   $94.90   $94.90  
  Purchase #2 $129.26   8.267%   $139.9459   $139.95   $139.95   $139.90  
  Purchase #3 $194.44   5.849%   $205.8128   $205.81   $205.80   $205.80  
  Purchase #4 $105.82   9.350%   $115.7142   $115.71   $115.70   $115.70  
  Purchase #5 $228.48   9.756%   $250.7705   $250.77   $250.75   $250.80  
  Purchase #6 $110.64   5.650%   $116.8912   $116.89   $116.90   $116.90  
  Purchase #7 $201.86   11.571%   $225.2172   $225.22   $225.20   $225.20  
  7 purchase totals = $1,058.18       $1,149.2672   $1,149.27   $1,149.20   $1,149.20