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 $122.66   11.769%   $137.0959   $137.10   $137.10   $137.10  
  Purchase #2 $175.48   10.814%   $194.4564   $194.46   $194.45   $194.50  
  Purchase #3 $96.51   7.279%   $103.535   $103.54   $103.55   $103.50  
  Purchase #4 $186.65   10.602%   $206.4386   $206.44   $206.45   $206.40  
  Purchase #5 $67.42   13.714%   $76.666   $76.67   $76.65   $76.70  
  Purchase #6 $156.77   13.805%   $178.4121   $178.41   $178.40   $178.40  
  Purchase #7 $118.37   9.650%   $129.7927   $129.79   $129.80   $129.80  
  7 purchase totals = $923.86       $1,026.3967   $1,026.41   $1,026.40   $1,026.40