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 $160.48   7.830%   $173.0456   $173.05   $173.05   $173.00  
  Purchase #2 $20.96   9.847%   $23.0239   $23.02   $23.00   $23.00  
  Purchase #3 $158.27   11.361%   $176.2511   $176.25   $176.25   $176.30  
  Purchase #4 $153.52   8.680%   $166.8455   $166.85   $166.85   $166.80  
  Purchase #5 $212.35   13.110%   $240.1891   $240.19   $240.20   $240.20  
  Purchase #6 $239.62   10.621%   $265.07   $265.07   $265.05   $265.10  
  Purchase #7 $8.84   8.419%   $9.5842   $9.58   $9.60   $9.60  
  7 purchase totals = $954.04       $1,054.0094   $1,054.01   $1,054.00   $1,054.00