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	$150.90	13.844%	$171.7906	$171.79	$171.80	$171.80
Purchase #2	$72.30	8.507%	$78.4506	$78.45	$78.45	$78.50
Purchase #3	$97.91	11.657%	$109.3234	$109.32	$109.30	$109.30
Purchase #4	$249.71	7.130%	$267.5143	$267.51	$267.50	$267.50
Purchase #5	$165.40	5.425%	$174.373	$174.37	$174.35	$174.40
Purchase #6	$165.83	9.436%	$181.4777	$181.48	$181.50	$181.50
Purchase #7	$152.97	13.870%	$174.1869	$174.19	$174.20	$174.20
7 purchase totals =	$1,055.02		$1,157.1165	$1,157.11	$1,157.10	$1,157.20