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 $216.83   11.234%   $241.1887   $241.19   $241.20   $241.20  
  Purchase #2 $190.44   6.743%   $203.2814   $203.28   $203.30   $203.30  
  Purchase #3 $80.72   8.409%   $87.5077   $87.51   $87.50   $87.50  
  Purchase #4 $102.34   5.346%   $107.8111   $107.81   $107.80   $107.80  
  Purchase #5 $106.85   8.626%   $116.0669   $116.07   $116.05   $116.10  
  Purchase #6 $212.40   9.146%   $231.8261   $231.83   $231.85   $231.80  
  Purchase #7 $193.63   8.609%   $210.2996   $210.30   $210.30   $210.30  
  7 purchase totals = $1,103.21       $1,197.9815   $1,197.99   $1,198.00   $1,198.00