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 $154.27   4.737%   $161.5778   $161.58   $161.60   $161.60  
  Purchase #2 $153.63   11.209%   $170.8504   $170.85   $170.85   $170.90  
  Purchase #3 $222.44   12.754%   $250.81   $250.81   $250.80   $250.80  
  Purchase #4 $129.92   6.362%   $138.1855   $138.19   $138.20   $138.20  
  Purchase #5 $250.50   4.530%   $261.8477   $261.85   $261.85   $261.80  
  Purchase #6 $43.70   5.178%   $45.9628   $45.96   $45.95   $46.00  
  Purchase #7 $39.34   3.106%   $40.5619   $40.56   $40.55   $40.60  
  7 purchase totals = $993.80       $1,069.7961   $1,069.80   $1,069.80   $1,069.90