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	$79.53	7.265%	$85.3079	$85.31	$85.30	$85.30
Purchase #2	$111.61	11.516%	$124.463	$124.46	$124.45	$124.50
Purchase #3	$136.85	9.625%	$150.0218	$150.02	$150.00	$150.00
Purchase #4	$61.89	3.751%	$64.2115	$64.21	$64.20	$64.20
Purchase #5	$81.51	12.421%	$91.6344	$91.63	$91.65	$91.60
Purchase #6	$81.39	4.802%	$85.2983	$85.30	$85.30	$85.30
Purchase #7	$85.73	10.124%	$94.4093	$94.41	$94.40	$94.40
7 purchase totals =	$638.51		$695.3462	$695.34	$695.30	$695.30