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 $165.96   13.567%   $188.4758   $188.48   $188.50   $188.50  
  Purchase #2 $114.27   10.316%   $126.0581   $126.06   $126.05   $126.10  
  Purchase #3 $47.65   8.564%   $51.7307   $51.73   $51.75   $51.70  
  Purchase #4 $246.58   12.589%   $277.622   $277.62   $277.60   $277.60  
  Purchase #5 $181.48   6.714%   $193.6646   $193.66   $193.65   $193.70  
  Purchase #6 $181.53   6.850%   $193.9648   $193.96   $193.95   $194.00  
  Purchase #7 $22.91   6.835%   $24.4759   $24.48   $24.50   $24.50  
  7 purchase totals = $960.38       $1,055.9919   $1,055.99   $1,056.00   $1,056.10