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	$41.38	4.721%	$43.3335	$43.33	$43.35	$43.30
Purchase #2	$35.67	9.393%	$39.0205	$39.02	$39.00	$39.00
Purchase #3	$202.53	3.350%	$209.3148	$209.31	$209.30	$209.30
Purchase #4	$198.36	12.369%	$222.8951	$222.90	$222.90	$222.90
Purchase #5	$106.93	11.530%	$119.259	$119.26	$119.25	$119.30
Purchase #6	$122.66	7.846%	$132.2839	$132.28	$132.30	$132.30
Purchase #7	$65.63	11.865%	$73.417	$73.42	$73.40	$73.40
7 purchase totals =	$773.16		$839.5238	$839.52	$839.50	$839.50