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	$80.79	12.426%	$90.829	$90.83	$90.85	$90.80
Purchase #2	$78.62	13.303%	$89.0788	$89.08	$89.10	$89.10
Purchase #3	$231.39	10.106%	$254.7743	$254.77	$254.75	$254.80
Purchase #4	$113.44	5.135%	$119.2651	$119.27	$119.25	$119.30
Purchase #5	$6.54	6.457%	$6.9623	$6.96	$6.95	$7.00
Purchase #6	$147.73	6.166%	$156.839	$156.84	$156.85	$156.80
Purchase #7	$179.93	3.809%	$186.7835	$186.78	$186.80	$186.80
7 purchase totals =	$838.44		$904.5320	$904.53	$904.55	$904.60