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 $9.31   5.418%   $9.8144   $9.81   $9.80   $9.80  
  Purchase #2 $222.26   9.222%   $242.7568   $242.76   $242.75   $242.80  
  Purchase #3 $9.28   12.769%   $10.465   $10.47   $10.45   $10.50  
  Purchase #4 $138.77   4.209%   $144.6108   $144.61   $144.60   $144.60  
  Purchase #5 $238.32   8.579%   $258.7655   $258.77   $258.75   $258.80  
  Purchase #6 $7.35   4.684%   $7.6943   $7.69   $7.70   $7.70  
  Purchase #7 $152.42   9.836%   $167.412   $167.41   $167.40   $167.40  
  7 purchase totals = $777.71       $841.5188   $841.52   $841.45   $841.60