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	$173.93	6.653%	$185.5016	$185.50	$185.50	$185.50
Purchase #2	$49.46	12.746%	$55.7642	$55.76	$55.75	$55.80
Purchase #3	$194.74	12.539%	$219.1584	$219.16	$219.15	$219.20
Purchase #4	$245.43	11.274%	$273.0998	$273.10	$273.10	$273.10
Purchase #5	$65.34	9.812%	$71.7512	$71.75	$71.75	$71.80
Purchase #6	$147.71	4.211%	$153.9301	$153.93	$153.95	$153.90
Purchase #7	$92.33	6.532%	$98.361	$98.36	$98.35	$98.40
7 purchase totals =	$968.94		$1,057.5663	$1,057.56	$1,057.55	$1,057.70