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	$64.96	13.137%	$73.4938	$73.49	$73.50	$73.50
Purchase #2	$188.72	11.227%	$209.9076	$209.91	$209.90	$209.90
Purchase #3	$75.78	12.770%	$85.4571	$85.46	$85.45	$85.50
Purchase #4	$216.58	7.570%	$232.9751	$232.98	$233.00	$233.00
Purchase #5	$65.94	9.740%	$72.3626	$72.36	$72.35	$72.40
Purchase #6	$210.59	5.439%	$222.044	$222.04	$222.05	$222.00
Purchase #7	$35.53	10.700%	$39.3317	$39.33	$39.35	$39.30
7 purchase totals =	$858.10		$935.5719	$935.57	$935.60	$935.60