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	$130.34	10.869%	$144.5067	$144.51	$144.50	$144.50
Purchase #2	$208.98	10.654%	$231.2447	$231.24	$231.25	$231.20
Purchase #3	$76.33	11.681%	$85.2461	$85.25	$85.25	$85.20
Purchase #4	$217.50	10.555%	$240.4571	$240.46	$240.45	$240.50
Purchase #5	$110.72	5.261%	$116.545	$116.55	$116.55	$116.50
Purchase #6	$127.33	9.543%	$139.4811	$139.48	$139.50	$139.50
Purchase #7	$189.50	9.404%	$207.3206	$207.32	$207.30	$207.30
7 purchase totals =	$1,060.70		$1,164.8013	$1,164.81	$1,164.80	$1,164.70