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 $84.56   13.321%   $95.8242   $95.82   $95.80   $95.80  
  Purchase #2 $156.79   11.428%   $174.708   $174.71   $174.70   $174.70  
  Purchase #3 $248.59   11.821%   $277.9758   $277.98   $278.00   $278.00  
  Purchase #4 $155.92   13.398%   $176.8102   $176.81   $176.80   $176.80  
  Purchase #5 $162.78   9.706%   $178.5794   $178.58   $178.60   $178.60  
  Purchase #6 $61.75   9.686%   $67.7311   $67.73   $67.75   $67.70  
  Purchase #7 $96.30   8.713%   $104.6906   $104.69   $104.70   $104.70  
  7 purchase totals = $966.69       $1,076.3193   $1,076.32   $1,076.35   $1,076.30