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	$7.47	11.465%	$8.3264	$8.33	$8.35	$8.30
Purchase #2	$142.61	7.214%	$152.8979	$152.90	$152.90	$152.90
Purchase #3	$149.65	11.463%	$166.8044	$166.80	$166.80	$166.80
Purchase #4	$59.25	10.428%	$65.4286	$65.43	$65.45	$65.40
Purchase #5	$78.43	9.148%	$85.6048	$85.60	$85.60	$85.60
Purchase #6	$210.86	8.114%	$227.9692	$227.97	$227.95	$228.00
Purchase #7	$201.69	7.781%	$217.3835	$217.38	$217.40	$217.40
7 purchase totals =	$849.96		$924.4148	$924.41	$924.45	$924.40