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	$85.34	4.473%	$89.1573	$89.16	$89.15	$89.20
Purchase #2	$73.88	11.548%	$82.4117	$82.41	$82.40	$82.40
Purchase #3	$234.80	5.668%	$248.1085	$248.11	$248.10	$248.10
Purchase #4	$109.54	5.824%	$115.9196	$115.92	$115.90	$115.90
Purchase #5	$44.65	8.320%	$48.3649	$48.36	$48.35	$48.40
Purchase #6	$84.77	11.297%	$94.3465	$94.35	$94.35	$94.30
Purchase #7	$79.88	10.808%	$88.5134	$88.51	$88.50	$88.50
7 purchase totals =	$712.86		$766.8219	$766.82	$766.75	$766.80