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	$54.36	12.782%	$61.3083	$61.31	$61.30	$61.30
Purchase #2	$210.43	6.376%	$223.847	$223.85	$223.85	$223.80
Purchase #3	$90.29	4.256%	$94.1327	$94.13	$94.15	$94.10
Purchase #4	$111.98	7.456%	$120.3292	$120.33	$120.35	$120.30
Purchase #5	$147.92	11.228%	$164.5285	$164.53	$164.55	$164.50
Purchase #6	$5.71	9.452%	$6.2497	$6.25	$6.25	$6.20
Purchase #7	$171.56	3.454%	$177.4857	$177.49	$177.50	$177.50
7 purchase totals =	$792.25		$847.8811	$847.89	$847.95	$847.70