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	$249.85	7.274%	$268.0241	$268.02	$268.00	$268.00
Purchase #2	$247.47	6.603%	$263.8104	$263.81	$263.80	$263.80
Purchase #3	$137.53	8.780%	$149.6051	$149.61	$149.60	$149.60
Purchase #4	$188.36	4.371%	$196.5932	$196.59	$196.60	$196.60
Purchase #5	$127.67	13.108%	$144.405	$144.41	$144.40	$144.40
Purchase #6	$7.97	7.740%	$8.5869	$8.59	$8.60	$8.60
Purchase #7	$89.44	8.179%	$96.7553	$96.76	$96.75	$96.80
7 purchase totals =	$1,048.29		$1,127.7800	$1,127.79	$1,127.75	$1,127.80