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	$203.48	6.390%	$216.4824	$216.48	$216.50	$216.50
Purchase #2	$117.56	9.570%	$128.8105	$128.81	$128.80	$128.80
Purchase #3	$93.41	6.221%	$99.221	$99.22	$99.20	$99.20
Purchase #4	$54.55	8.521%	$59.1982	$59.20	$59.20	$59.20
Purchase #5	$59.63	9.538%	$65.3175	$65.32	$65.30	$65.30
Purchase #6	$42.66	12.252%	$47.8867	$47.89	$47.90	$47.90
Purchase #7	$210.99	3.470%	$218.3114	$218.31	$218.30	$218.30
7 purchase totals =	$782.28		$835.2277	$835.23	$835.20	$835.20