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 $23.49   10.671%   $25.9966   $26.00   $26.00   $26.00  
  Purchase #2 $18.41   6.111%   $19.535   $19.54   $19.55   $19.50  
  Purchase #3 $138.72   12.157%   $155.5842   $155.58   $155.60   $155.60  
  Purchase #4 $152.98   5.603%   $161.5515   $161.55   $161.55   $161.60  
  Purchase #5 $227.76   9.175%   $248.657   $248.66   $248.65   $248.70  
  Purchase #6 $94.81   4.501%   $99.0774   $99.08   $99.10   $99.10  
  Purchase #7 $45.38   12.862%   $51.2168   $51.22   $51.20   $51.20  
  7 purchase totals = $701.55       $761.6185   $761.63   $761.65   $761.70