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	$78.72	4.346%	$82.1412	$82.14	$82.15	$82.10
Purchase #2	$177.32	3.836%	$184.122	$184.12	$184.10	$184.10
Purchase #3	$104.75	5.266%	$110.2661	$110.27	$110.25	$110.30
Purchase #4	$228.58	9.436%	$250.1488	$250.15	$250.15	$250.10
Purchase #5	$135.41	4.271%	$141.1934	$141.19	$141.20	$141.20
Purchase #6	$79.81	7.190%	$85.5483	$85.55	$85.55	$85.50
Purchase #7	$22.81	13.513%	$25.8923	$25.89	$25.90	$25.90
7 purchase totals =	$827.40		$879.3121	$879.31	$879.30	$879.20