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 $53.87   4.411%   $56.2462   $56.25   $56.25   $56.20  
  Purchase #2 $105.68   13.356%   $119.7946   $119.79   $119.80   $119.80  
  Purchase #3 $89.34   7.702%   $96.221   $96.22   $96.20   $96.20  
  Purchase #4 $25.53   7.465%   $27.4358   $27.44   $27.45   $27.40  
  Purchase #5 $104.57   9.643%   $114.6537   $114.65   $114.65   $114.70  
  Purchase #6 $144.27   13.282%   $163.4319   $163.43   $163.45   $163.40  
  Purchase #7 $115.28   4.724%   $120.7258   $120.73   $120.75   $120.70  
  7 purchase totals = $638.54       $698.5090   $698.51   $698.55   $698.40