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 $22.95   6.791%   $24.5085   $24.51   $24.50   $24.50  
  Purchase #2 $92.30   13.245%   $104.5251   $104.53   $104.55   $104.50  
  Purchase #3 $83.52   10.434%   $92.2345   $92.23   $92.25   $92.20  
  Purchase #4 $23.48   11.180%   $26.1051   $26.11   $26.10   $26.10  
  Purchase #5 $236.57   10.506%   $261.424   $261.42   $261.40   $261.40  
  Purchase #6 $228.36   10.701%   $252.7968   $252.80   $252.80   $252.80  
  Purchase #7 $156.54   12.470%   $176.0605   $176.06   $176.05   $176.10  
  7 purchase totals = $843.72       $937.6545   $937.66   $937.65   $937.60