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	$250.76	13.411%	$284.3894	$284.39	$284.40	$284.40
Purchase #2	$17.90	13.462%	$20.3097	$20.31	$20.30	$20.30
Purchase #3	$240.71	9.312%	$263.1249	$263.12	$263.10	$263.10
Purchase #4	$122.96	5.151%	$129.2937	$129.29	$129.30	$129.30
Purchase #5	$98.97	6.270%	$105.1754	$105.18	$105.20	$105.20
Purchase #6	$198.33	6.295%	$210.8149	$210.81	$210.80	$210.80
Purchase #7	$168.40	11.120%	$187.1261	$187.13	$187.15	$187.10
7 purchase totals =	$1,098.03		$1,200.2341	$1,200.23	$1,200.25	$1,200.20