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	$89.68	11.790%	$100.2533	$100.25	$100.25	$100.30
Purchase #2	$91.99	13.476%	$104.3866	$104.39	$104.40	$104.40
Purchase #3	$159.89	6.148%	$169.72	$169.72	$169.70	$169.70
Purchase #4	$216.92	5.654%	$229.1847	$229.18	$229.20	$229.20
Purchase #5	$140.72	13.497%	$159.713	$159.71	$159.70	$159.70
Purchase #6	$91.82	4.578%	$96.0235	$96.02	$96.00	$96.00
Purchase #7	$29.36	6.649%	$31.3121	$31.31	$31.30	$31.30
7 purchase totals =	$820.38		$890.5932	$890.58	$890.55	$890.60