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	$79.26	5.823%	$83.8753	$83.88	$83.90	$83.90
Purchase #2	$185.32	5.841%	$196.1445	$196.14	$196.15	$196.10
Purchase #3	$201.96	8.145%	$218.4096	$218.41	$218.40	$218.40
Purchase #4	$196.70	9.490%	$215.3668	$215.37	$215.35	$215.40
Purchase #5	$35.54	4.782%	$37.2395	$37.24	$37.25	$37.20
Purchase #6	$51.98	13.368%	$58.9287	$58.93	$58.95	$58.90
Purchase #7	$139.64	5.506%	$147.3286	$147.33	$147.35	$147.30
7 purchase totals =	$890.40		$957.2930	$957.30	$957.35	$957.20