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 $203.56   10.519%   $224.9725   $224.97   $224.95   $225.00  
  Purchase #2 $201.27   3.677%   $208.6707   $208.67   $208.65   $208.70  
  Purchase #3 $152.45   9.405%   $166.7879   $166.79   $166.80   $166.80  
  Purchase #4 $248.68   6.172%   $264.0285   $264.03   $264.05   $264.00  
  Purchase #5 $223.28   3.815%   $231.7981   $231.80   $231.80   $231.80  
  Purchase #6 $206.26   4.102%   $214.7208   $214.72   $214.70   $214.70  
  Purchase #7 $13.36   11.289%   $14.8682   $14.87   $14.85   $14.90  
  7 purchase totals = $1,248.86       $1,325.8467   $1,325.85   $1,325.80   $1,325.90