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	$18.92	11.525%	$21.1005	$21.10	$21.10	$21.10
Purchase #2	$53.72	11.272%	$59.7753	$59.78	$59.80	$59.80
Purchase #3	$36.54	3.266%	$37.7334	$37.73	$37.75	$37.70
Purchase #4	$135.65	9.753%	$148.8799	$148.88	$148.90	$148.90
Purchase #5	$103.36	12.690%	$116.4764	$116.48	$116.50	$116.50
Purchase #6	$226.61	6.254%	$240.7822	$240.78	$240.80	$240.80
Purchase #7	$125.54	6.474%	$133.6675	$133.67	$133.65	$133.70
7 purchase totals =	$700.34		$758.4152	$758.42	$758.50	$758.50