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	$125.52	13.277%	$142.1853	$142.19	$142.20	$142.20
Purchase #2	$189.90	3.494%	$196.5351	$196.54	$196.55	$196.50
Purchase #3	$237.29	5.438%	$250.1938	$250.19	$250.20	$250.20
Purchase #4	$146.44	10.652%	$162.0388	$162.04	$162.05	$162.00
Purchase #5	$13.52	3.154%	$13.9464	$13.95	$13.95	$13.90
Purchase #6	$84.45	7.529%	$90.8082	$90.81	$90.80	$90.80
Purchase #7	$216.61	13.241%	$245.2913	$245.29	$245.30	$245.30
7 purchase totals =	$1,013.73		$1,100.9989	$1,101.01	$1,101.05	$1,100.90