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	$131.76	13.734%	$149.8559	$149.86	$149.85	$149.90
Purchase #2	$233.73	5.165%	$245.8022	$245.80	$245.80	$245.80
Purchase #3	$205.55	5.443%	$216.7381	$216.74	$216.75	$216.70
Purchase #4	$201.98	13.675%	$229.6008	$229.60	$229.60	$229.60
Purchase #5	$6.38	3.359%	$6.5943	$6.59	$6.60	$6.60
Purchase #6	$78.96	13.359%	$89.5083	$89.51	$89.50	$89.50
Purchase #7	$31.58	4.631%	$33.0425	$33.04	$33.05	$33.00
7 purchase totals =	$889.94		$971.1421	$971.14	$971.15	$971.10