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	$121.94	5.311%	$128.4162	$128.42	$128.40	$128.40
Purchase #2	$81.36	3.686%	$84.3589	$84.36	$84.35	$84.40
Purchase #3	$142.96	4.130%	$148.8642	$148.86	$148.85	$148.90
Purchase #4	$120.33	9.282%	$131.499	$131.50	$131.50	$131.50
Purchase #5	$31.70	3.797%	$32.9036	$32.90	$32.90	$32.90
Purchase #6	$29.40	11.463%	$32.7701	$32.77	$32.75	$32.80
Purchase #7	$219.59	11.816%	$245.5368	$245.54	$245.55	$245.50
7 purchase totals =	$747.28		$804.3488	$804.35	$804.30	$804.40