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	$40.74	3.527%	$42.1769	$42.18	$42.20	$42.20
Purchase #2	$28.66	8.331%	$31.0477	$31.05	$31.05	$31.00
Purchase #3	$223.57	13.332%	$253.3764	$253.38	$253.40	$253.40
Purchase #4	$84.82	7.175%	$90.9058	$90.91	$90.90	$90.90
Purchase #5	$218.25	3.847%	$226.6461	$226.65	$226.65	$226.60
Purchase #6	$81.53	4.581%	$85.2649	$85.26	$85.25	$85.30
Purchase #7	$170.33	10.753%	$188.6456	$188.65	$188.65	$188.60
7 purchase totals =	$847.90		$918.0634	$918.08	$918.10	$918.00