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	$242.38	11.545%	$270.3628	$270.36	$270.35	$270.40
Purchase #2	$198.53	13.687%	$225.7028	$225.70	$225.70	$225.70
Purchase #3	$164.46	12.648%	$185.2609	$185.26	$185.25	$185.30
Purchase #4	$103.48	5.862%	$109.546	$109.55	$109.55	$109.50
Purchase #5	$54.74	9.442%	$59.9086	$59.91	$59.90	$59.90
Purchase #6	$197.97	5.687%	$209.2286	$209.23	$209.25	$209.20
Purchase #7	$239.60	7.429%	$257.3999	$257.40	$257.40	$257.40
7 purchase totals =	$1,201.16		$1,317.4096	$1,317.41	$1,317.40	$1,317.40