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	$178.39	12.381%	$200.4765	$200.48	$200.50	$200.50
Purchase #2	$98.57	6.794%	$105.2668	$105.27	$105.25	$105.30
Purchase #3	$182.96	3.130%	$188.6866	$188.69	$188.70	$188.70
Purchase #4	$196.43	12.494%	$220.972	$220.97	$220.95	$221.00
Purchase #5	$84.64	3.430%	$87.5432	$87.54	$87.55	$87.50
Purchase #6	$127.79	6.316%	$135.8612	$135.86	$135.85	$135.90
Purchase #7	$166.57	3.714%	$172.7564	$172.76	$172.75	$172.80
7 purchase totals =	$1,035.35		$1,111.5627	$1,111.57	$1,111.55	$1,111.70