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	$72.67	12.160%	$81.5067	$81.51	$81.50	$81.50
Purchase #2	$162.27	4.110%	$168.9393	$168.94	$168.95	$168.90
Purchase #3	$211.74	11.103%	$235.2495	$235.25	$235.25	$235.20
Purchase #4	$40.54	6.780%	$43.2886	$43.29	$43.30	$43.30
Purchase #5	$48.61	5.622%	$51.3429	$51.34	$51.35	$51.30
Purchase #6	$38.31	11.613%	$42.7589	$42.76	$42.75	$42.80
Purchase #7	$85.41	7.809%	$92.0797	$92.08	$92.10	$92.10
7 purchase totals =	$659.55		$715.1656	$715.17	$715.20	$715.10