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 $76.76   9.249%   $83.8595   $83.86   $83.85   $83.90  
  Purchase #2 $35.63   3.482%   $36.8706   $36.87   $36.85   $36.90  
  Purchase #3 $174.30   4.246%   $181.7008   $181.70   $181.70   $181.70  
  Purchase #4 $245.49   6.109%   $260.487   $260.49   $260.50   $260.50  
  Purchase #5 $172.56   3.524%   $178.641   $178.64   $178.65   $178.60  
  Purchase #6 $226.80   11.455%   $252.7799   $252.78   $252.80   $252.80  
  Purchase #7 $195.64   13.741%   $222.5229   $222.52   $222.50   $222.50  
  7 purchase totals = $1,127.18       $1,216.8617   $1,216.86   $1,216.85   $1,216.90