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 $88.74   8.172%   $95.9918   $95.99   $96.00   $96.00  
  Purchase #2 $212.92   13.656%   $241.9964   $242.00   $242.00   $242.00  
  Purchase #3 $62.81   6.329%   $66.7852   $66.79   $66.80   $66.80  
  Purchase #4 $36.49   7.158%   $39.102   $39.10   $39.10   $39.10  
  Purchase #5 $127.83   7.693%   $137.664   $137.66   $137.65   $137.70  
  Purchase #6 $164.58   6.768%   $175.7188   $175.72   $175.70   $175.70  
  Purchase #7 $100.31   9.514%   $109.8535   $109.85   $109.85   $109.90  
  7 purchase totals = $793.68       $867.1117   $867.11   $867.10   $867.20