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 $212.28   13.536%   $241.0142   $241.01   $241.00   $241.00  
  Purchase #2 $197.35   8.139%   $213.4123   $213.41   $213.40   $213.40  
  Purchase #3 $166.86   9.535%   $182.7701   $182.77   $182.75   $182.80  
  Purchase #4 $124.96   13.544%   $141.8846   $141.88   $141.90   $141.90  
  Purchase #5 $154.33   8.208%   $166.9974   $167.00   $167.00   $167.00  
  Purchase #6 $49.80   5.601%   $52.5893   $52.59   $52.60   $52.60  
  Purchase #7 $131.93   3.629%   $136.7177   $136.72   $136.70   $136.70  
  7 purchase totals = $1,037.51       $1,135.3856   $1,135.38   $1,135.35   $1,135.40