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	$137.70	12.210%	$154.5132	$154.51	$154.50	$154.50
Purchase #2	$105.90	6.430%	$112.7094	$112.71	$112.70	$112.70
Purchase #3	$90.89	11.325%	$101.1833	$101.18	$101.20	$101.20
Purchase #4	$84.74	13.339%	$96.0435	$96.04	$96.05	$96.00
Purchase #5	$209.56	12.572%	$235.9059	$235.91	$235.90	$235.90
Purchase #6	$152.99	9.868%	$168.0871	$168.09	$168.10	$168.10
Purchase #7	$136.27	4.119%	$141.883	$141.88	$141.90	$141.90
7 purchase totals =	$918.05		$1,010.3254	$1,010.32	$1,010.35	$1,010.30