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	$19.67	4.512%	$20.5575	$20.56	$20.55	$20.60
Purchase #2	$176.67	3.645%	$183.1096	$183.11	$183.10	$183.10
Purchase #3	$133.41	8.180%	$144.3229	$144.32	$144.30	$144.30
Purchase #4	$195.29	4.141%	$203.377	$203.38	$203.40	$203.40
Purchase #5	$225.67	5.673%	$238.4723	$238.47	$238.45	$238.50
Purchase #6	$89.88	7.124%	$96.2831	$96.28	$96.30	$96.30
Purchase #7	$184.72	3.555%	$191.2868	$191.29	$191.30	$191.30
7 purchase totals =	$1,025.31		$1,077.4092	$1,077.41	$1,077.40	$1,077.50