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 $25.31   5.756%   $26.7668   $26.77   $26.75   $26.80  
  Purchase #2 $155.89   3.807%   $161.8247   $161.82   $161.80   $161.80  
  Purchase #3 $228.40   13.316%   $258.8137   $258.81   $258.80   $258.80  
  Purchase #4 $102.95   13.832%   $117.19   $117.19   $117.20   $117.20  
  Purchase #5 $93.57   11.781%   $104.5935   $104.59   $104.60   $104.60  
  Purchase #6 $232.98   9.309%   $254.6681   $254.67   $254.65   $254.70  
  Purchase #7 $145.85   4.428%   $152.3082   $152.31   $152.30   $152.30  
  7 purchase totals = $984.95       $1,076.1650   $1,076.16   $1,076.10   $1,076.20