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 $81.26   13.619%   $92.3268   $92.33   $92.35   $92.30  
  Purchase #2 $225.76   9.376%   $246.9273   $246.93   $246.95   $246.90  
  Purchase #3 $117.85   6.710%   $125.7577   $125.76   $125.75   $125.80  
  Purchase #4 $75.79   11.660%   $84.6271   $84.63   $84.65   $84.60  
  Purchase #5 $47.92   11.874%   $53.61   $53.61   $53.60   $53.60  
  Purchase #6 $165.59   13.172%   $187.4015   $187.40   $187.40   $187.40  
  Purchase #7 $201.69   6.288%   $214.3723   $214.37   $214.35   $214.40  
  7 purchase totals = $915.86       $1,005.0227   $1,005.03   $1,005.05   $1,005.00