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 $68.49   11.526%   $76.3842   $76.38   $76.40   $76.40  
  Purchase #2 $212.99   8.793%   $231.7182   $231.72   $231.70   $231.70  
  Purchase #3 $211.25   9.737%   $231.8194   $231.82   $231.80   $231.80  
  Purchase #4 $73.47   8.533%   $79.7392   $79.74   $79.75   $79.70  
  Purchase #5 $150.49   9.840%   $165.2982   $165.30   $165.30   $165.30  
  Purchase #6 $201.59   7.175%   $216.0541   $216.05   $216.05   $216.10  
  Purchase #7 $49.89   12.800%   $56.2759   $56.28   $56.30   $56.30  
  7 purchase totals = $968.17       $1,057.2892   $1,057.29   $1,057.30   $1,057.30