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	$138.84	12.299%	$155.9159	$155.92	$155.90	$155.90
Purchase #2	$82.31	8.244%	$89.0956	$89.10	$89.10	$89.10
Purchase #3	$159.49	13.160%	$180.4789	$180.48	$180.50	$180.50
Purchase #4	$136.53	11.401%	$152.0958	$152.10	$152.10	$152.10
Purchase #5	$152.87	4.191%	$159.2768	$159.28	$159.30	$159.30
Purchase #6	$140.77	4.427%	$147.0019	$147.00	$147.00	$147.00
Purchase #7	$175.74	3.577%	$182.0262	$182.03	$182.05	$182.00
7 purchase totals =	$986.55		$1,065.8911	$1,065.91	$1,065.95	$1,065.90