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	$79.58	11.691%	$88.8837	$88.88	$88.90	$88.90
Purchase #2	$249.90	5.861%	$264.5466	$264.55	$264.55	$264.50
Purchase #3	$207.73	6.654%	$221.5524	$221.55	$221.55	$221.60
Purchase #4	$25.43	10.136%	$28.0076	$28.01	$28.00	$28.00
Purchase #5	$39.42	5.466%	$41.5747	$41.57	$41.55	$41.60
Purchase #6	$211.30	7.212%	$226.539	$226.54	$226.55	$226.50
Purchase #7	$210.40	9.218%	$229.7947	$229.79	$229.80	$229.80
7 purchase totals =	$1,023.76		$1,100.8987	$1,100.89	$1,100.90	$1,100.90