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	$246.35	3.318%	$254.5239	$254.52	$254.50	$254.50
Purchase #2	$140.46	9.254%	$153.4582	$153.46	$153.45	$153.50
Purchase #3	$99.80	12.462%	$112.2371	$112.24	$112.25	$112.20
Purchase #4	$33.90	3.786%	$35.1835	$35.18	$35.20	$35.20
Purchase #5	$127.63	11.665%	$142.518	$142.52	$142.50	$142.50
Purchase #6	$125.38	9.638%	$137.4641	$137.46	$137.45	$137.50
Purchase #7	$186.58	10.708%	$206.559	$206.56	$206.55	$206.60
7 purchase totals =	$960.10		$1,041.9438	$1,041.94	$1,041.90	$1,042.00