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 $172.89   13.310%   $195.9017   $195.90   $195.90   $195.90  
  Purchase #2 $149.69   5.242%   $157.5367   $157.54   $157.55   $157.50  
  Purchase #3 $46.54   8.738%   $50.6067   $50.61   $50.60   $50.60  
  Purchase #4 $36.62   8.432%   $39.7078   $39.71   $39.70   $39.70  
  Purchase #5 $193.80   10.719%   $214.5734   $214.57   $214.55   $214.60  
  Purchase #6 $237.57   12.783%   $267.9386   $267.94   $267.95   $267.90  
  Purchase #7 $97.81   8.400%   $106.026   $106.03   $106.05   $106.00  
  7 purchase totals = $934.92       $1,032.2909   $1,032.30   $1,032.30   $1,032.20