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 $84.78   10.298%   $93.5106   $93.51   $93.50   $93.50  
  Purchase #2 $24.78   7.661%   $26.6784   $26.68   $26.70   $26.70  
  Purchase #3 $157.53   7.144%   $168.7839   $168.78   $168.80   $168.80  
  Purchase #4 $127.49   5.577%   $134.6001   $134.60   $134.60   $134.60  
  Purchase #5 $236.29   5.133%   $248.4188   $248.42   $248.40   $248.40  
  Purchase #6 $197.75   6.555%   $210.7125   $210.71   $210.70   $210.70  
  Purchase #7 $18.79   4.444%   $19.625   $19.63   $19.65   $19.60  
  7 purchase totals = $847.41       $902.3293   $902.33   $902.35   $902.30