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 $184.65   4.411%   $192.7949   $192.79   $192.80   $192.80  
  Purchase #2 $154.35   5.505%   $162.847   $162.85   $162.85   $162.80  
  Purchase #3 $56.44   7.377%   $60.6036   $60.60   $60.60   $60.60  
  Purchase #4 $140.76   10.301%   $155.2597   $155.26   $155.25   $155.30  
  Purchase #5 $130.85   7.484%   $140.6428   $140.64   $140.65   $140.60  
  Purchase #6 $184.52   7.266%   $197.9272   $197.93   $197.95   $197.90  
  Purchase #7 $80.52   4.522%   $84.1611   $84.16   $84.15   $84.20  
  7 purchase totals = $932.09       $994.2363   $994.23   $994.25   $994.20