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	$160.86	5.312%	$169.4049	$169.40	$169.40	$169.40
Purchase #2	$190.46	7.317%	$204.396	$204.40	$204.40	$204.40
Purchase #3	$159.73	13.172%	$180.7696	$180.77	$180.75	$180.80
Purchase #4	$91.74	13.179%	$103.8304	$103.83	$103.85	$103.80
Purchase #5	$229.96	8.707%	$249.9826	$249.98	$250.00	$250.00
Purchase #6	$184.87	6.281%	$196.4817	$196.48	$196.50	$196.50
Purchase #7	$132.39	6.489%	$140.9808	$140.98	$141.00	$141.00
7 purchase totals =	$1,150.01		$1,245.8460	$1,245.84	$1,245.90	$1,245.90