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	$37.30	9.554%	$40.8636	$40.86	$40.85	$40.90
Purchase #2	$125.63	4.230%	$130.9441	$130.94	$130.95	$130.90
Purchase #3	$145.59	7.225%	$156.1089	$156.11	$156.10	$156.10
Purchase #4	$41.26	9.170%	$45.0435	$45.04	$45.05	$45.00
Purchase #5	$134.72	13.250%	$152.5704	$152.57	$152.55	$152.60
Purchase #6	$77.76	5.718%	$82.2063	$82.21	$82.20	$82.20
Purchase #7	$229.28	6.812%	$244.8986	$244.90	$244.90	$244.90
7 purchase totals =	$791.54		$852.6354	$852.63	$852.60	$852.60