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	$179.76	3.370%	$185.8179	$185.82	$185.80	$185.80
Purchase #2	$170.63	8.749%	$185.5584	$185.56	$185.55	$185.60
Purchase #3	$164.26	6.562%	$175.0387	$175.04	$175.05	$175.00
Purchase #4	$25.32	7.699%	$27.2694	$27.27	$27.25	$27.30
Purchase #5	$92.54	5.673%	$97.7898	$97.79	$97.80	$97.80
Purchase #6	$236.33	11.841%	$264.3138	$264.31	$264.30	$264.30
Purchase #7	$132.76	12.552%	$149.424	$149.42	$149.40	$149.40
7 purchase totals =	$1,001.60		$1,085.2120	$1,085.21	$1,085.15	$1,085.20