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	$225.45	11.561%	$251.5143	$251.51	$251.50	$251.50
Purchase #2	$170.90	9.310%	$186.8108	$186.81	$186.80	$186.80
Purchase #3	$12.46	8.496%	$13.5186	$13.52	$13.50	$13.50
Purchase #4	$80.92	10.802%	$89.661	$89.66	$89.65	$89.70
Purchase #5	$227.90	11.595%	$254.325	$254.33	$254.35	$254.30
Purchase #6	$147.30	6.373%	$156.6874	$156.69	$156.70	$156.70
Purchase #7	$72.27	9.749%	$79.3156	$79.32	$79.30	$79.30
7 purchase totals =	$937.20		$1,031.8327	$1,031.84	$1,031.80	$1,031.80