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 $220.95   11.726%   $246.8586   $246.86   $246.85   $246.90  
  Purchase #2 $29.67   11.248%   $33.0073   $33.01   $33.00   $33.00  
  Purchase #3 $78.41   11.580%   $87.4899   $87.49   $87.50   $87.50  
  Purchase #4 $102.34   4.283%   $106.7232   $106.72   $106.70   $106.70  
  Purchase #5 $33.36   10.349%   $36.8124   $36.81   $36.80   $36.80  
  Purchase #6 $130.72   10.602%   $144.5789   $144.58   $144.60   $144.60  
  Purchase #7 $113.38   7.426%   $121.7996   $121.80   $121.80   $121.80  
  7 purchase totals = $708.83       $777.2699   $777.27   $777.25   $777.30