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	$19.34	7.823%	$20.853	$20.85	$20.85	$20.90
Purchase #2	$96.73	6.764%	$103.2728	$103.27	$103.25	$103.30
Purchase #3	$99.97	10.192%	$110.1589	$110.16	$110.15	$110.20
Purchase #4	$245.94	11.328%	$273.8001	$273.80	$273.80	$273.80
Purchase #5	$94.78	10.709%	$104.93	$104.93	$104.95	$104.90
Purchase #6	$142.31	12.366%	$159.9081	$159.91	$159.90	$159.90
Purchase #7	$250.74	10.587%	$277.2858	$277.29	$277.30	$277.30
7 purchase totals =	$949.81		$1,050.2087	$1,050.21	$1,050.20	$1,050.30