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 $57.53   9.840%   $63.191   $63.19   $63.20   $63.20  
  Purchase #2 $83.47   10.820%   $92.5015   $92.50   $92.50   $92.50  
  Purchase #3 $85.86   12.439%   $96.5401   $96.54   $96.55   $96.50  
  Purchase #4 $175.25   7.858%   $189.0211   $189.02   $189.00   $189.00  
  Purchase #5 $233.92   5.851%   $247.6067   $247.61   $247.60   $247.60  
  Purchase #6 $239.54   12.124%   $268.5818   $268.58   $268.60   $268.60  
  Purchase #7 $15.59   6.272%   $16.5678   $16.57   $16.55   $16.60  
  7 purchase totals = $891.16       $974.0100   $974.01   $974.00   $974.00