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	$185.75	3.279%	$191.8407	$191.84	$191.85	$191.80
Purchase #2	$97.39	6.641%	$103.8577	$103.86	$103.85	$103.90
Purchase #3	$85.58	3.201%	$88.3194	$88.32	$88.30	$88.30
Purchase #4	$121.73	12.626%	$137.0996	$137.10	$137.10	$137.10
Purchase #5	$118.35	4.777%	$124.0036	$124.00	$124.00	$124.00
Purchase #6	$30.90	3.216%	$31.8937	$31.89	$31.90	$31.90
Purchase #7	$58.28	10.724%	$64.5299	$64.53	$64.55	$64.50
7 purchase totals =	$697.98		$741.5446	$741.54	$741.55	$741.50