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	$196.47	12.445%	$220.9207	$220.92	$220.90	$220.90
Purchase #2	$109.67	12.337%	$123.2	$123.20	$123.20	$123.20
Purchase #3	$228.71	4.451%	$238.8899	$238.89	$238.90	$238.90
Purchase #4	$136.81	5.453%	$144.2702	$144.27	$144.25	$144.30
Purchase #5	$130.29	13.319%	$147.6433	$147.64	$147.65	$147.60
Purchase #6	$230.78	5.603%	$243.7106	$243.71	$243.70	$243.70
Purchase #7	$124.73	4.179%	$129.9425	$129.94	$129.95	$129.90
7 purchase totals =	$1,157.46		$1,248.5772	$1,248.57	$1,248.55	$1,248.50