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	$98.39	6.385%	$104.6722	$104.67	$104.65	$104.70
Purchase #2	$222.65	10.146%	$245.2401	$245.24	$245.25	$245.20
Purchase #3	$175.75	7.815%	$189.4849	$189.48	$189.50	$189.50
Purchase #4	$167.35	8.765%	$182.0182	$182.02	$182.00	$182.00
Purchase #5	$31.57	7.513%	$33.9419	$33.94	$33.95	$33.90
Purchase #6	$203.77	9.713%	$223.5622	$223.56	$223.55	$223.60
Purchase #7	$52.77	13.567%	$59.9293	$59.93	$59.95	$59.90
7 purchase totals =	$952.25		$1,038.8488	$1,038.84	$1,038.85	$1,038.80