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	$89.92	10.202%	$99.0936	$99.09	$99.10	$99.10
Purchase #2	$247.67	5.790%	$262.0101	$262.01	$262.00	$262.00
Purchase #3	$207.31	7.687%	$223.2459	$223.25	$223.25	$223.20
Purchase #4	$243.78	10.215%	$268.6821	$268.68	$268.70	$268.70
Purchase #5	$79.55	12.526%	$89.5144	$89.51	$89.50	$89.50
Purchase #6	$133.36	10.796%	$147.7575	$147.76	$147.75	$147.80
Purchase #7	$48.96	3.775%	$50.8082	$50.81	$50.80	$50.80
7 purchase totals =	$1,050.55		$1,141.1118	$1,141.11	$1,141.10	$1,141.10