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 $176.38   11.536%   $196.7272   $196.73   $196.75   $196.70  
  Purchase #2 $169.99   10.139%   $187.2253   $187.23   $187.25   $187.20  
  Purchase #3 $214.93   10.224%   $236.9044   $236.90   $236.90   $236.90  
  Purchase #4 $24.87   12.295%   $27.9278   $27.93   $27.95   $27.90  
  Purchase #5 $61.62   12.632%   $69.4038   $69.40   $69.40   $69.40  
  Purchase #6 $209.96   4.473%   $219.3515   $219.35   $219.35   $219.40  
  Purchase #7 $169.40   12.663%   $190.8511   $190.85   $190.85   $190.90  
  7 purchase totals = $1,027.15       $1,128.3911   $1,128.39   $1,128.45   $1,128.40