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	$133.89	11.616%	$149.4427	$149.44	$149.45	$149.40
Purchase #2	$148.79	12.666%	$167.6357	$167.64	$167.65	$167.60
Purchase #3	$40.68	4.239%	$42.4044	$42.40	$42.40	$42.40
Purchase #4	$150.31	6.825%	$160.5687	$160.57	$160.55	$160.60
Purchase #5	$118.71	8.288%	$128.5487	$128.55	$128.55	$128.50
Purchase #6	$89.85	4.299%	$93.7127	$93.71	$93.70	$93.70
Purchase #7	$110.36	11.515%	$123.068	$123.07	$123.05	$123.10
7 purchase totals =	$792.59		$865.3809	$865.38	$865.35	$865.30