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	$54.81	5.394%	$57.7665	$57.77	$57.75	$57.80
Purchase #2	$101.91	8.343%	$110.4124	$110.41	$110.40	$110.40
Purchase #3	$167.25	12.307%	$187.8335	$187.83	$187.85	$187.80
Purchase #4	$102.50	8.673%	$111.3898	$111.39	$111.40	$111.40
Purchase #5	$209.38	4.362%	$218.5132	$218.51	$218.50	$218.50
Purchase #6	$134.65	4.219%	$140.3309	$140.33	$140.35	$140.30
Purchase #7	$168.42	4.223%	$175.5324	$175.53	$175.55	$175.50
7 purchase totals =	$938.92		$1,001.7787	$1,001.77	$1,001.80	$1,001.70