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	$82.71	7.480%	$88.8967	$88.90	$88.90	$88.90
Purchase #2	$194.32	13.734%	$221.0079	$221.01	$221.00	$221.00
Purchase #3	$6.98	11.387%	$7.7748	$7.77	$7.75	$7.80
Purchase #4	$106.94	4.562%	$111.8186	$111.82	$111.80	$111.80
Purchase #5	$249.68	5.755%	$264.0491	$264.05	$264.05	$264.00
Purchase #6	$105.45	5.219%	$110.9534	$110.95	$110.95	$111.00
Purchase #7	$31.92	3.179%	$32.9347	$32.93	$32.95	$32.90
7 purchase totals =	$778.00		$837.4352	$837.43	$837.40	$837.40