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	$80.57	11.150%	$89.5536	$89.55	$89.55	$89.60
Purchase #2	$33.80	9.230%	$36.9197	$36.92	$36.90	$36.90
Purchase #3	$99.69	11.711%	$111.3647	$111.36	$111.35	$111.40
Purchase #4	$168.32	10.437%	$185.8876	$185.89	$185.90	$185.90
Purchase #5	$111.89	12.625%	$126.0161	$126.02	$126.00	$126.00
Purchase #6	$237.51	6.660%	$253.3282	$253.33	$253.35	$253.30
Purchase #7	$124.93	13.124%	$141.3258	$141.33	$141.35	$141.30
7 purchase totals =	$856.71		$944.3957	$944.40	$944.40	$944.40