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 $62.45   9.452%   $68.3528   $68.35   $68.35   $68.40  
  Purchase #2 $173.55   7.719%   $186.9463   $186.95   $186.95   $186.90  
  Purchase #3 $155.60   7.836%   $167.7928   $167.79   $167.80   $167.80  
  Purchase #4 $248.65   6.337%   $264.407   $264.41   $264.40   $264.40  
  Purchase #5 $238.75   12.108%   $267.6579   $267.66   $267.65   $267.70  
  Purchase #6 $208.72   3.336%   $215.6829   $215.68   $215.70   $215.70  
  Purchase #7 $20.95   13.862%   $23.8541   $23.85   $23.85   $23.90  
  7 purchase totals = $1,108.67       $1,194.6938   $1,194.69   $1,194.70   $1,194.80