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 $41.25   12.865%   $46.5568   $46.56   $46.55   $46.60  
  Purchase #2 $99.77   8.506%   $108.2564   $108.26   $108.25   $108.30  
  Purchase #3 $198.55   5.455%   $209.3809   $209.38   $209.40   $209.40  
  Purchase #4 $57.92   8.150%   $62.6405   $62.64   $62.65   $62.60  
  Purchase #5 $234.75   13.378%   $266.1549   $266.15   $266.15   $266.20  
  Purchase #6 $220.51   4.597%   $230.6468   $230.65   $230.65   $230.60  
  Purchase #7 $107.32   12.192%   $120.4045   $120.40   $120.40   $120.40  
  7 purchase totals = $960.07       $1,044.0408   $1,044.04   $1,044.05   $1,044.10