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	$79.30	5.708%	$83.8264	$83.83	$83.85	$83.80
Purchase #2	$73.83	3.413%	$76.3498	$76.35	$76.35	$76.30
Purchase #3	$88.36	12.366%	$99.2866	$99.29	$99.30	$99.30
Purchase #4	$189.38	12.540%	$213.1283	$213.13	$213.15	$213.10
Purchase #5	$52.33	13.765%	$59.5332	$59.53	$59.55	$59.50
Purchase #6	$233.67	6.695%	$249.3142	$249.31	$249.30	$249.30
Purchase #7	$159.27	5.443%	$167.9391	$167.94	$167.95	$167.90
7 purchase totals =	$876.14		$949.3776	$949.38	$949.45	$949.20