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	$42.98	5.432%	$45.3147	$45.31	$45.30	$45.30
Purchase #2	$46.44	8.620%	$50.4431	$50.44	$50.45	$50.40
Purchase #3	$200.38	5.287%	$210.9741	$210.97	$210.95	$211.00
Purchase #4	$215.52	6.648%	$229.8478	$229.85	$229.85	$229.80
Purchase #5	$6.34	3.433%	$6.5577	$6.56	$6.55	$6.60
Purchase #6	$200.74	4.559%	$209.8917	$209.89	$209.90	$209.90
Purchase #7	$191.85	12.208%	$215.271	$215.27	$215.25	$215.30
7 purchase totals =	$904.25		$968.3001	$968.29	$968.25	$968.30