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	$86.29	5.644%	$91.1602	$91.16	$91.15	$91.20
Purchase #2	$242.72	3.320%	$250.7783	$250.78	$250.80	$250.80
Purchase #3	$177.78	7.874%	$191.7784	$191.78	$191.80	$191.80
Purchase #4	$175.89	12.383%	$197.6705	$197.67	$197.65	$197.70
Purchase #5	$75.42	8.793%	$82.0517	$82.05	$82.05	$82.10
Purchase #6	$171.71	10.441%	$189.6382	$189.64	$189.65	$189.60
Purchase #7	$81.93	9.723%	$89.8961	$89.90	$89.90	$89.90
7 purchase totals =	$1,011.74		$1,092.9734	$1,092.98	$1,093.00	$1,093.10