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 $31.60   7.555%   $33.9874   $33.99   $34.00   $34.00  
  Purchase #2 $149.27   5.269%   $157.135   $157.14   $157.15   $157.10  
  Purchase #3 $177.39   6.248%   $188.4733   $188.47   $188.45   $188.50  
  Purchase #4 $197.62   4.210%   $205.9398   $205.94   $205.95   $205.90  
  Purchase #5 $195.28   7.416%   $209.762   $209.76   $209.75   $209.80  
  Purchase #6 $61.70   5.379%   $65.0188   $65.02   $65.00   $65.00  
  Purchase #7 $145.83   13.202%   $165.0825   $165.08   $165.10   $165.10  
  7 purchase totals = $958.69       $1,025.3988   $1,025.40   $1,025.40   $1,025.40