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 $46.66   8.402%   $50.5804   $50.58   $50.60   $50.60  
  Purchase #2 $214.96   8.788%   $233.8507   $233.85   $233.85   $233.90  
  Purchase #3 $201.67   10.846%   $223.5431   $223.54   $223.55   $223.50  
  Purchase #4 $53.73   12.563%   $60.4801   $60.48   $60.50   $60.50  
  Purchase #5 $221.30   12.577%   $249.1329   $249.13   $249.15   $249.10  
  Purchase #6 $170.82   13.815%   $194.4188   $194.42   $194.40   $194.40  
  Purchase #7 $224.31   4.631%   $234.6978   $234.70   $234.70   $234.70  
  7 purchase totals = $1,133.45       $1,246.7038   $1,246.70   $1,246.75   $1,246.70