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	$68.33	5.830%	$72.3136	$72.31	$72.30	$72.30
Purchase #2	$61.44	13.525%	$69.7498	$69.75	$69.75	$69.70
Purchase #3	$60.73	10.865%	$67.3283	$67.33	$67.35	$67.30
Purchase #4	$156.86	6.755%	$167.4559	$167.46	$167.45	$167.50
Purchase #5	$98.59	9.371%	$107.8289	$107.83	$107.85	$107.80
Purchase #6	$167.27	13.459%	$189.7829	$189.78	$189.80	$189.80
Purchase #7	$133.68	6.236%	$142.0163	$142.02	$142.00	$142.00
7 purchase totals =	$746.90		$816.4757	$816.48	$816.50	$816.40