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	$115.34	7.427%	$123.9063	$123.91	$123.90	$123.90
Purchase #2	$162.58	10.118%	$179.0298	$179.03	$179.05	$179.00
Purchase #3	$202.77	7.723%	$218.4299	$218.43	$218.45	$218.40
Purchase #4	$201.54	5.757%	$213.1427	$213.14	$213.15	$213.10
Purchase #5	$126.37	10.241%	$139.3116	$139.31	$139.30	$139.30
Purchase #6	$99.55	11.615%	$111.1127	$111.11	$111.10	$111.10
Purchase #7	$88.53	11.873%	$99.0412	$99.04	$99.05	$99.00
7 purchase totals =	$996.68		$1,083.9742	$1,083.97	$1,084.00	$1,083.80