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	$99.72	13.494%	$113.1762	$113.18	$113.20	$113.20
Purchase #2	$129.33	12.288%	$145.2221	$145.22	$145.20	$145.20
Purchase #3	$12.74	13.598%	$14.4724	$14.47	$14.45	$14.50
Purchase #4	$134.62	6.760%	$143.7203	$143.72	$143.70	$143.70
Purchase #5	$246.64	11.455%	$274.8926	$274.89	$274.90	$274.90
Purchase #6	$139.45	12.512%	$156.898	$156.90	$156.90	$156.90
Purchase #7	$211.46	12.801%	$238.529	$238.53	$238.55	$238.50
7 purchase totals =	$973.96		$1,086.9106	$1,086.91	$1,086.90	$1,086.90