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 $176.60   7.548%   $189.9298   $189.93   $189.95   $189.90  
  Purchase #2 $134.87   3.625%   $139.759   $139.76   $139.75   $139.80  
  Purchase #3 $66.77   6.643%   $71.2055   $71.21   $71.20   $71.20  
  Purchase #4 $7.70   11.637%   $8.596   $8.60   $8.60   $8.60  
  Purchase #5 $69.79   11.458%   $77.7865   $77.79   $77.80   $77.80  
  Purchase #6 $171.59   11.191%   $190.7926   $190.79   $190.80   $190.80  
  Purchase #7 $87.39   3.454%   $90.4085   $90.41   $90.40   $90.40  
  7 purchase totals = $714.71       $768.4779   $768.49   $768.50   $768.50