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	$93.38	7.412%	$100.3013	$100.30	$100.30	$100.30
Purchase #2	$125.64	6.466%	$133.7639	$133.76	$133.75	$133.80
Purchase #3	$81.93	9.485%	$89.7011	$89.70	$89.70	$89.70
Purchase #4	$230.73	12.441%	$259.4351	$259.44	$259.45	$259.40
Purchase #5	$209.48	8.473%	$227.2292	$227.23	$227.25	$227.20
Purchase #6	$195.95	6.393%	$208.4771	$208.48	$208.50	$208.50
Purchase #7	$83.50	10.586%	$92.3393	$92.34	$92.35	$92.30
7 purchase totals =	$1,020.61		$1,111.2470	$1,111.25	$1,111.30	$1,111.20