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 $169.61   10.581%   $187.5564   $187.56   $187.55   $187.60  
  Purchase #2 $47.59   12.408%   $53.495   $53.50   $53.50   $53.50  
  Purchase #3 $78.92   5.579%   $83.3229   $83.32   $83.30   $83.30  
  Purchase #4 $160.35   9.665%   $175.8478   $175.85   $175.85   $175.80  
  Purchase #5 $103.99   13.351%   $117.8737   $117.87   $117.85   $117.90  
  Purchase #6 $26.50   10.616%   $29.3132   $29.31   $29.30   $29.30  
  Purchase #7 $162.99   4.707%   $170.6619   $170.66   $170.65   $170.70  
  7 purchase totals = $749.95       $818.0709   $818.07   $818.00   $818.10