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 $44.47   6.121%   $47.192   $47.19   $47.20   $47.20  
  Purchase #2 $202.68   10.459%   $223.8783   $223.88   $223.90   $223.90  
  Purchase #3 $46.53   7.239%   $49.8983   $49.90   $49.90   $49.90  
  Purchase #4 $60.81   5.139%   $63.935   $63.94   $63.95   $63.90  
  Purchase #5 $158.90   13.638%   $180.5708   $180.57   $180.55   $180.60  
  Purchase #6 $124.80   9.353%   $136.4725   $136.47   $136.45   $136.50  
  Purchase #7 $34.98   6.781%   $37.352   $37.35   $37.35   $37.40  
  7 purchase totals = $673.17       $739.2989   $739.30   $739.30   $739.40