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 $187.43   10.224%   $206.5928   $206.59   $206.60   $206.60  
  Purchase #2 $240.40   9.747%   $263.8318   $263.83   $263.85   $263.80  
  Purchase #3 $156.77   10.514%   $173.2528   $173.25   $173.25   $173.30  
  Purchase #4 $19.36   13.484%   $21.9705   $21.97   $21.95   $22.00  
  Purchase #5 $122.33   12.335%   $137.4194   $137.42   $137.40   $137.40  
  Purchase #6 $114.67   11.789%   $128.1884   $128.19   $128.20   $128.20  
  Purchase #7 $63.58   5.799%   $67.267   $67.27   $67.25   $67.30  
  7 purchase totals = $904.54       $998.5227   $998.52   $998.50   $998.60