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	$85.88	6.334%	$91.3196	$91.32	$91.30	$91.30
Purchase #2	$198.95	5.854%	$210.5965	$210.60	$210.60	$210.60
Purchase #3	$101.90	13.108%	$115.2571	$115.26	$115.25	$115.30
Purchase #4	$72.59	11.360%	$80.8362	$80.84	$80.85	$80.80
Purchase #5	$136.74	4.284%	$142.5979	$142.60	$142.60	$142.60
Purchase #6	$53.41	11.121%	$59.3497	$59.35	$59.35	$59.30
Purchase #7	$22.27	9.181%	$24.3146	$24.31	$24.30	$24.30
7 purchase totals =	$671.74		$724.2716	$724.28	$724.25	$724.20