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	$219.73	13.794%	$250.0396	$250.04	$250.05	$250.00
Purchase #2	$200.98	5.132%	$211.2943	$211.29	$211.30	$211.30
Purchase #3	$33.59	12.120%	$37.6611	$37.66	$37.65	$37.70
Purchase #4	$121.41	5.427%	$127.9989	$128.00	$128.00	$128.00
Purchase #5	$109.90	3.378%	$113.6124	$113.61	$113.60	$113.60
Purchase #6	$125.47	12.222%	$140.8049	$140.80	$140.80	$140.80
Purchase #7	$191.69	10.275%	$211.3861	$211.39	$211.40	$211.40
7 purchase totals =	$1,002.77		$1,092.7973	$1,092.79	$1,092.80	$1,092.80