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 $144.87   10.587%   $160.2074   $160.21   $160.20   $160.20  
  Purchase #2 $247.47   12.239%   $277.7579   $277.76   $277.75   $277.80  
  Purchase #3 $17.97   7.145%   $19.254   $19.25   $19.25   $19.30  
  Purchase #4 $118.95   9.255%   $129.9588   $129.96   $129.95   $130.00  
  Purchase #5 $68.81   8.329%   $74.5412   $74.54   $74.55   $74.50  
  Purchase #6 $12.26   11.360%   $13.6527   $13.65   $13.65   $13.70  
  Purchase #7 $27.66   9.577%   $30.309   $30.31   $30.30   $30.30  
  7 purchase totals = $637.99       $705.6810   $705.68   $705.65   $705.80