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	$222.54	12.215%	$249.7233	$249.72	$249.70	$249.70
Purchase #2	$85.53	4.499%	$89.378	$89.38	$89.40	$89.40
Purchase #3	$139.78	7.872%	$150.7835	$150.78	$150.80	$150.80
Purchase #4	$120.95	3.181%	$124.7974	$124.80	$124.80	$124.80
Purchase #5	$35.33	6.218%	$37.5268	$37.53	$37.55	$37.50
Purchase #6	$75.53	3.340%	$78.0527	$78.05	$78.05	$78.10
Purchase #7	$57.41	12.865%	$64.7958	$64.80	$64.80	$64.80
7 purchase totals =	$737.07		$795.0575	$795.06	$795.10	$795.10