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	$91.99	13.196%	$104.129	$104.13	$104.15	$104.10
Purchase #2	$171.76	6.556%	$183.0206	$183.02	$183.00	$183.00
Purchase #3	$96.72	13.263%	$109.548	$109.55	$109.55	$109.50
Purchase #4	$250.58	5.815%	$265.1512	$265.15	$265.15	$265.20
Purchase #5	$33.84	12.683%	$38.1319	$38.13	$38.15	$38.10
Purchase #6	$134.73	3.424%	$139.3432	$139.34	$139.35	$139.30
Purchase #7	$28.39	11.152%	$31.5561	$31.56	$31.55	$31.60
7 purchase totals =	$808.01		$870.8800	$870.88	$870.90	$870.80