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	$34.40	10.258%	$37.9288	$37.93	$37.95	$37.90
Purchase #2	$158.89	6.226%	$168.7825	$168.78	$168.80	$168.80
Purchase #3	$35.35	11.557%	$39.4354	$39.44	$39.45	$39.40
Purchase #4	$161.94	12.219%	$181.7274	$181.73	$181.75	$181.70
Purchase #5	$208.59	6.344%	$221.8229	$221.82	$221.80	$221.80
Purchase #6	$171.48	10.207%	$188.983	$188.98	$189.00	$189.00
Purchase #7	$166.65	5.105%	$175.1575	$175.16	$175.15	$175.20
7 purchase totals =	$937.30		$1,013.8375	$1,013.84	$1,013.90	$1,013.80