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	$172.66	12.443%	$194.1441	$194.14	$194.15	$194.10
Purchase #2	$141.31	6.721%	$150.8074	$150.81	$150.80	$150.80
Purchase #3	$168.38	7.472%	$180.9614	$180.96	$180.95	$181.00
Purchase #4	$108.57	8.234%	$117.5097	$117.51	$117.50	$117.50
Purchase #5	$198.37	3.407%	$205.1285	$205.13	$205.15	$205.10
Purchase #6	$115.72	13.412%	$131.2404	$131.24	$131.25	$131.20
Purchase #7	$37.90	6.740%	$40.4545	$40.45	$40.45	$40.50
7 purchase totals =	$942.91		$1,020.2460	$1,020.24	$1,020.25	$1,020.20