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	$81.53	11.807%	$91.1562	$91.16	$91.15	$91.20
Purchase #2	$132.56	9.184%	$144.7343	$144.73	$144.75	$144.70
Purchase #3	$55.59	6.668%	$59.2967	$59.30	$59.30	$59.30
Purchase #4	$217.55	5.419%	$229.339	$229.34	$229.35	$229.30
Purchase #5	$125.55	13.458%	$142.4465	$142.45	$142.45	$142.40
Purchase #6	$25.51	10.279%	$28.1322	$28.13	$28.15	$28.10
Purchase #7	$147.45	10.172%	$162.4486	$162.45	$162.45	$162.40
7 purchase totals =	$785.74		$857.5535	$857.56	$857.60	$857.40