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 $245.38   6.769%   $261.9898   $261.99   $262.00   $262.00  
  Purchase #2 $212.58   7.849%   $229.2654   $229.27   $229.25   $229.30  
  Purchase #3 $143.56   5.154%   $150.9591   $150.96   $150.95   $151.00  
  Purchase #4 $84.81   6.841%   $90.6119   $90.61   $90.60   $90.60  
  Purchase #5 $76.88   11.606%   $85.8027   $85.80   $85.80   $85.80  
  Purchase #6 $111.42   6.709%   $118.8952   $118.90   $118.90   $118.90  
  Purchase #7 $36.55   5.811%   $38.6739   $38.67   $38.65   $38.70  
  7 purchase totals = $911.18       $976.1980   $976.20   $976.15   $976.30