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 $126.40   6.712%   $134.884   $134.88   $134.90   $134.90  
  Purchase #2 $58.76   4.551%   $61.4342   $61.43   $61.45   $61.40  
  Purchase #3 $77.62   6.396%   $82.5846   $82.58   $82.60   $82.60  
  Purchase #4 $149.35   10.469%   $164.9855   $164.99   $165.00   $165.00  
  Purchase #5 $179.54   11.230%   $199.7023   $199.70   $199.70   $199.70  
  Purchase #6 $209.85   11.391%   $233.754   $233.75   $233.75   $233.80  
  Purchase #7 $68.32   6.355%   $72.6617   $72.66   $72.65   $72.70  
  7 purchase totals = $869.84       $950.0063   $949.99   $950.05   $950.10