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	$7.67	6.131%	$8.1402	$8.14	$8.15	$8.10
Purchase #2	$156.82	3.616%	$162.4906	$162.49	$162.50	$162.50
Purchase #3	$34.85	6.650%	$37.1675	$37.17	$37.15	$37.20
Purchase #4	$135.60	12.487%	$152.5324	$152.53	$152.55	$152.50
Purchase #5	$76.99	7.281%	$82.5956	$82.60	$82.60	$82.60
Purchase #6	$193.39	9.578%	$211.9129	$211.91	$211.90	$211.90
Purchase #7	$115.38	12.682%	$130.0125	$130.01	$130.00	$130.00
7 purchase totals =	$720.70		$784.8517	$784.85	$784.85	$784.80