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 $156.42   3.704%   $162.2138   $162.21   $162.20   $162.20  
  Purchase #2 $160.30   7.439%   $172.2247   $172.22   $172.20   $172.20  
  Purchase #3 $87.44   4.157%   $91.0749   $91.07   $91.05   $91.10  
  Purchase #4 $171.83   7.315%   $184.3994   $184.40   $184.40   $184.40  
  Purchase #5 $170.87   7.834%   $184.256   $184.26   $184.25   $184.30  
  Purchase #6 $155.60   8.557%   $168.9147   $168.91   $168.90   $168.90  
  Purchase #7 $129.36   7.421%   $138.9598   $138.96   $138.95   $139.00  
  7 purchase totals = $1,031.82       $1,102.0433   $1,102.03   $1,101.95   $1,102.10