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	$243.50	6.431%	$259.1595	$259.16	$259.15	$259.20
Purchase #2	$65.33	6.782%	$69.7607	$69.76	$69.75	$69.80
Purchase #3	$198.56	8.762%	$215.9578	$215.96	$215.95	$216.00
Purchase #4	$36.72	9.667%	$40.2697	$40.27	$40.25	$40.30
Purchase #5	$69.59	13.112%	$78.7146	$78.71	$78.70	$78.70
Purchase #6	$166.58	8.483%	$180.711	$180.71	$180.70	$180.70
Purchase #7	$156.42	11.682%	$174.693	$174.69	$174.70	$174.70
7 purchase totals =	$936.70		$1,019.2663	$1,019.26	$1,019.20	$1,019.40