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	$106.31	13.809%	$120.9903	$120.99	$121.00	$121.00
Purchase #2	$29.34	3.869%	$30.4752	$30.48	$30.50	$30.50
Purchase #3	$81.90	8.811%	$89.1162	$89.12	$89.10	$89.10
Purchase #4	$124.86	5.362%	$131.555	$131.56	$131.55	$131.60
Purchase #5	$157.55	9.144%	$171.9564	$171.96	$171.95	$172.00
Purchase #6	$139.25	8.273%	$150.7702	$150.77	$150.75	$150.80
Purchase #7	$246.85	11.158%	$274.3935	$274.39	$274.40	$274.40
7 purchase totals =	$886.06		$969.2568	$969.27	$969.25	$969.40