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	$18.54	6.689%	$19.7801	$19.78	$19.80	$19.80
Purchase #2	$51.45	3.300%	$53.1479	$53.15	$53.15	$53.10
Purchase #3	$106.46	6.229%	$113.0914	$113.09	$113.10	$113.10
Purchase #4	$59.69	12.521%	$67.1638	$67.16	$67.15	$67.20
Purchase #5	$131.78	11.870%	$147.4223	$147.42	$147.40	$147.40
Purchase #6	$223.57	9.186%	$244.1071	$244.11	$244.10	$244.10
Purchase #7	$231.36	5.387%	$243.8234	$243.82	$243.80	$243.80
7 purchase totals =	$822.85		$888.5360	$888.53	$888.50	$888.50