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 $47.63   13.218%   $53.9257   $53.93   $53.95   $53.90  
  Purchase #2 $198.34   8.336%   $214.8736   $214.87   $214.85   $214.90  
  Purchase #3 $68.80   3.104%   $70.9356   $70.94   $70.95   $70.90  
  Purchase #4 $215.51   13.492%   $244.5866   $244.59   $244.60   $244.60  
  Purchase #5 $225.78   8.842%   $245.7435   $245.74   $245.75   $245.70  
  Purchase #6 $170.82   12.560%   $192.275   $192.28   $192.30   $192.30  
  Purchase #7 $80.35   12.376%   $90.2941   $90.29   $90.30   $90.30  
  7 purchase totals = $1,007.23       $1,112.6341   $1,112.64   $1,112.70   $1,112.60