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	$225.46	5.634%	$238.1624	$238.16	$238.15	$238.20
Purchase #2	$246.40	11.425%	$274.5512	$274.55	$274.55	$274.60
Purchase #3	$71.76	13.322%	$81.3199	$81.32	$81.30	$81.30
Purchase #4	$175.83	7.709%	$189.3847	$189.38	$189.40	$189.40
Purchase #5	$171.63	11.160%	$190.7839	$190.78	$190.80	$190.80
Purchase #6	$120.44	10.443%	$133.0175	$133.02	$133.00	$133.00
Purchase #7	$195.86	10.238%	$215.9121	$215.91	$215.90	$215.90
7 purchase totals =	$1,207.38		$1,323.1317	$1,323.12	$1,323.10	$1,323.20