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	$84.76	7.265%	$90.9178	$90.92	$90.90	$90.90
Purchase #2	$248.34	13.347%	$281.4859	$281.49	$281.50	$281.50
Purchase #3	$179.92	3.192%	$185.663	$185.66	$185.65	$185.70
Purchase #4	$67.98	4.819%	$71.256	$71.26	$71.25	$71.30
Purchase #5	$125.95	8.452%	$136.5953	$136.60	$136.60	$136.60
Purchase #6	$157.87	8.337%	$171.0316	$171.03	$171.05	$171.00
Purchase #7	$39.36	3.820%	$40.8636	$40.86	$40.85	$40.90
7 purchase totals =	$904.18		$977.8132	$977.82	$977.80	$977.90