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 $192.56   6.741%   $205.5405   $205.54   $205.55   $205.50  
  Purchase #2 $173.26   13.270%   $196.2516   $196.25   $196.25   $196.30  
  Purchase #3 $76.33   4.197%   $79.5336   $79.53   $79.55   $79.50  
  Purchase #4 $250.45   6.767%   $267.398   $267.40   $267.40   $267.40  
  Purchase #5 $22.64   11.109%   $25.1551   $25.16   $25.15   $25.20  
  Purchase #6 $218.38   6.483%   $232.5376   $232.54   $232.55   $232.50  
  Purchase #7 $69.49   3.241%   $71.7422   $71.74   $71.75   $71.70  
  7 purchase totals = $1,003.11       $1,078.1586   $1,078.16   $1,078.20   $1,078.10