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	$160.91	5.279%	$169.4044	$169.40	$169.40	$169.40
Purchase #2	$236.37	13.466%	$268.1996	$268.20	$268.20	$268.20
Purchase #3	$58.73	12.415%	$66.0213	$66.02	$66.00	$66.00
Purchase #4	$160.46	6.277%	$170.5321	$170.53	$170.55	$170.50
Purchase #5	$98.67	13.398%	$111.8898	$111.89	$111.90	$111.90
Purchase #6	$7.35	7.392%	$7.8933	$7.89	$7.90	$7.90
Purchase #7	$39.89	4.148%	$41.5446	$41.54	$41.55	$41.50
7 purchase totals =	$762.38		$835.4851	$835.47	$835.50	$835.40