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	$36.30	9.790%	$39.8538	$39.85	$39.85	$39.90
Purchase #2	$205.61	5.382%	$216.6759	$216.68	$216.70	$216.70
Purchase #3	$134.48	9.394%	$147.1131	$147.11	$147.10	$147.10
Purchase #4	$143.28	13.658%	$162.8492	$162.85	$162.85	$162.80
Purchase #5	$125.56	12.669%	$141.4672	$141.47	$141.45	$141.50
Purchase #6	$166.89	11.285%	$185.7235	$185.72	$185.70	$185.70
Purchase #7	$221.99	12.717%	$250.2205	$250.22	$250.20	$250.20
7 purchase totals =	$1,034.11		$1,143.9032	$1,143.90	$1,143.85	$1,143.90