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 $103.49   10.320%   $114.1702   $114.17   $114.15   $114.20  
  Purchase #2 $65.39   3.743%   $67.8375   $67.84   $67.85   $67.80  
  Purchase #3 $248.65   6.481%   $264.765   $264.77   $264.75   $264.80  
  Purchase #4 $161.62   12.392%   $181.648   $181.65   $181.65   $181.60  
  Purchase #5 $193.91   5.419%   $204.418   $204.42   $204.40   $204.40  
  Purchase #6 $63.76   13.484%   $72.3574   $72.36   $72.35   $72.40  
  Purchase #7 $36.85   4.327%   $38.4445   $38.44   $38.45   $38.40  
  7 purchase totals = $873.67       $943.6406   $943.65   $943.60   $943.60