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 $25.49   3.256%   $26.32   $26.32   $26.30   $26.30  
  Purchase #2 $171.77   5.464%   $181.1555   $181.16   $181.15   $181.20  
  Purchase #3 $246.80   8.755%   $268.4073   $268.41   $268.40   $268.40  
  Purchase #4 $90.40   3.299%   $93.3823   $93.38   $93.40   $93.40  
  Purchase #5 $29.75   8.726%   $32.346   $32.35   $32.35   $32.30  
  Purchase #6 $226.28   4.210%   $235.8064   $235.81   $235.80   $235.80  
  Purchase #7 $156.65   9.505%   $171.5396   $171.54   $171.55   $171.50  
  7 purchase totals = $947.14       $1,008.9571   $1,008.97   $1,008.95   $1,008.90