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	$39.31	9.321%	$42.9741	$42.97	$42.95	$43.00
Purchase #2	$84.47	10.481%	$93.3233	$93.32	$93.30	$93.30
Purchase #3	$36.88	10.559%	$40.7742	$40.77	$40.75	$40.80
Purchase #4	$61.69	5.157%	$64.8714	$64.87	$64.85	$64.90
Purchase #5	$201.86	4.286%	$210.5117	$210.51	$210.50	$210.50
Purchase #6	$91.67	4.415%	$95.7172	$95.72	$95.70	$95.70
Purchase #7	$136.86	11.473%	$152.5619	$152.56	$152.55	$152.60
7 purchase totals =	$652.74		$700.7338	$700.72	$700.60	$700.80