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 $147.63   3.702%   $153.0953   $153.10   $153.10   $153.10  
  Purchase #2 $78.67   9.436%   $86.0933   $86.09   $86.10   $86.10  
  Purchase #3 $54.43   6.561%   $58.0012   $58.00   $58.00   $58.00  
  Purchase #4 $114.73   4.382%   $119.7575   $119.76   $119.75   $119.80  
  Purchase #5 $177.91   5.534%   $187.7555   $187.76   $187.75   $187.80  
  Purchase #6 $232.49   10.475%   $256.8433   $256.84   $256.85   $256.80  
  Purchase #7 $223.60   12.683%   $251.9592   $251.96   $251.95   $252.00  
  7 purchase totals = $1,029.46       $1,113.5053   $1,113.51   $1,113.50   $1,113.60