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	$99.43	11.788%	$111.1508	$111.15	$111.15	$111.20
Purchase #2	$82.46	3.389%	$85.2546	$85.25	$85.25	$85.30
Purchase #3	$171.33	12.799%	$193.2585	$193.26	$193.25	$193.30
Purchase #4	$163.59	12.112%	$183.404	$183.40	$183.40	$183.40
Purchase #5	$206.31	12.578%	$232.2597	$232.26	$232.25	$232.30
Purchase #6	$178.57	5.357%	$188.136	$188.14	$188.15	$188.10
Purchase #7	$143.31	3.155%	$147.8314	$147.83	$147.85	$147.80
7 purchase totals =	$1,045.00		$1,141.2950	$1,141.29	$1,141.30	$1,141.40