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 $222.36   7.161%   $238.2832   $238.28   $238.30   $238.30  
  Purchase #2 $204.46   13.620%   $232.3075   $232.31   $232.30   $232.30  
  Purchase #3 $12.90   6.194%   $13.699   $13.70   $13.70   $13.70  
  Purchase #4 $60.68   10.256%   $66.9033   $66.90   $66.90   $66.90  
  Purchase #5 $174.44   4.249%   $181.852   $181.85   $181.85   $181.90  
  Purchase #6 $117.61   11.448%   $131.074   $131.07   $131.05   $131.10  
  Purchase #7 $170.56   8.107%   $184.3873   $184.39   $184.40   $184.40  
  7 purchase totals = $963.01       $1,048.5063   $1,048.50   $1,048.50   $1,048.60