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	$76.30	11.819%	$85.3179	$85.32	$85.30	$85.30
Purchase #2	$71.31	3.710%	$73.9556	$73.96	$73.95	$74.00
Purchase #3	$110.42	9.163%	$120.5378	$120.54	$120.55	$120.50
Purchase #4	$59.40	13.285%	$67.2913	$67.29	$67.30	$67.30
Purchase #5	$141.45	5.565%	$149.3217	$149.32	$149.30	$149.30
Purchase #6	$114.89	11.729%	$128.3654	$128.37	$128.35	$128.40
Purchase #7	$191.92	7.364%	$206.053	$206.05	$206.05	$206.10
7 purchase totals =	$765.69		$830.8427	$830.85	$830.80	$830.90