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	$69.46	5.737%	$73.4449	$73.44	$73.45	$73.40
Purchase #2	$228.32	7.263%	$244.9029	$244.90	$244.90	$244.90
Purchase #3	$19.79	3.527%	$20.488	$20.49	$20.50	$20.50
Purchase #4	$156.59	5.385%	$165.0224	$165.02	$165.00	$165.00
Purchase #5	$156.30	9.677%	$171.4252	$171.43	$171.45	$171.40
Purchase #6	$67.61	5.432%	$71.2826	$71.28	$71.30	$71.30
Purchase #7	$211.95	13.810%	$241.2203	$241.22	$241.20	$241.20
7 purchase totals =	$910.02		$987.7863	$987.78	$987.80	$987.70