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	$121.51	6.108%	$128.9318	$128.93	$128.95	$128.90
Purchase #2	$73.44	6.721%	$78.3759	$78.38	$78.40	$78.40
Purchase #3	$16.57	13.782%	$18.8537	$18.85	$18.85	$18.90
Purchase #4	$228.56	5.803%	$241.8233	$241.82	$241.80	$241.80
Purchase #5	$89.34	11.211%	$99.3559	$99.36	$99.35	$99.40
Purchase #6	$201.56	10.259%	$222.238	$222.24	$222.25	$222.20
Purchase #7	$148.97	11.371%	$165.9094	$165.91	$165.90	$165.90
7 purchase totals =	$879.95		$955.4880	$955.49	$955.50	$955.50