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	$209.31	6.226%	$222.3416	$222.34	$222.35	$222.30
Purchase #2	$235.28	7.857%	$253.7659	$253.77	$253.75	$253.80
Purchase #3	$110.92	8.700%	$120.57	$120.57	$120.55	$120.60
Purchase #4	$101.40	9.867%	$111.4051	$111.41	$111.40	$111.40
Purchase #5	$86.70	6.832%	$92.6233	$92.62	$92.60	$92.60
Purchase #6	$205.73	11.555%	$229.5021	$229.50	$229.50	$229.50
Purchase #7	$90.96	11.287%	$101.2267	$101.23	$101.25	$101.20
7 purchase totals =	$1,040.30		$1,131.4347	$1,131.44	$1,131.40	$1,131.40