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 $232.82   8.543%   $252.7098   $252.71   $252.70   $252.70  
  Purchase #2 $61.86   10.819%   $68.5526   $68.55   $68.55   $68.60  
  Purchase #3 $171.25   5.369%   $180.4444   $180.44   $180.45   $180.40  
  Purchase #4 $246.34   8.801%   $268.0204   $268.02   $268.00   $268.00  
  Purchase #5 $41.39   6.702%   $44.164   $44.16   $44.15   $44.20  
  Purchase #6 $76.32   4.172%   $79.5041   $79.50   $79.50   $79.50  
  Purchase #7 $52.85   8.177%   $57.1715   $57.17   $57.15   $57.20  
  7 purchase totals = $882.83       $950.5668   $950.55   $950.50   $950.60