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	$73.77	6.533%	$78.5894	$78.59	$78.60	$78.60
Purchase #2	$209.90	10.469%	$231.8744	$231.87	$231.85	$231.90
Purchase #3	$44.37	3.360%	$45.8608	$45.86	$45.85	$45.90
Purchase #4	$130.99	4.125%	$136.3933	$136.39	$136.40	$136.40
Purchase #5	$43.29	6.764%	$46.2181	$46.22	$46.20	$46.20
Purchase #6	$167.34	7.867%	$180.5046	$180.50	$180.50	$180.50
Purchase #7	$89.29	7.853%	$96.3019	$96.30	$96.30	$96.30
7 purchase totals =	$758.95		$815.7425	$815.73	$815.70	$815.80