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	$180.26	13.316%	$204.2634	$204.26	$204.25	$204.30
Purchase #2	$168.69	9.711%	$185.0715	$185.07	$185.05	$185.10
Purchase #3	$135.94	4.666%	$142.283	$142.28	$142.30	$142.30
Purchase #4	$48.71	5.282%	$51.2829	$51.28	$51.30	$51.30
Purchase #5	$64.50	10.504%	$71.2751	$71.28	$71.30	$71.30
Purchase #6	$70.66	11.690%	$78.9202	$78.92	$78.90	$78.90
Purchase #7	$240.33	3.304%	$248.2705	$248.27	$248.25	$248.30
7 purchase totals =	$909.09		$981.3666	$981.36	$981.35	$981.50