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	$184.88	4.531%	$193.2569	$193.26	$193.25	$193.30
Purchase #2	$177.48	6.810%	$189.5664	$189.57	$189.55	$189.60
Purchase #3	$78.59	4.495%	$82.1226	$82.12	$82.10	$82.10
Purchase #4	$94.82	12.761%	$106.92	$106.92	$106.90	$106.90
Purchase #5	$134.86	7.797%	$145.375	$145.38	$145.40	$145.40
Purchase #6	$79.93	11.729%	$89.305	$89.31	$89.30	$89.30
Purchase #7	$43.33	10.414%	$47.8424	$47.84	$47.85	$47.80
7 purchase totals =	$793.89		$854.3883	$854.40	$854.35	$854.40