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 $175.94   8.119%   $190.2246   $190.22   $190.20   $190.20  
  Purchase #2 $212.28   10.822%   $235.2529   $235.25   $235.25   $235.30  
  Purchase #3 $169.34   7.380%   $181.8373   $181.84   $181.85   $181.80  
  Purchase #4 $67.45   12.779%   $76.0694   $76.07   $76.05   $76.10  
  Purchase #5 $101.93   11.663%   $113.8181   $113.82   $113.80   $113.80  
  Purchase #6 $8.86   8.184%   $9.5851   $9.59   $9.60   $9.60  
  Purchase #7 $248.77   7.276%   $266.8705   $266.87   $266.85   $266.90  
  7 purchase totals = $984.57       $1,073.6579   $1,073.66   $1,073.60   $1,073.70