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 $29.88   13.779%   $33.9972   $34.00   $34.00   $34.00  
  Purchase #2 $106.66   8.605%   $115.8381   $115.84   $115.85   $115.80  
  Purchase #3 $36.94   12.171%   $41.436   $41.44   $41.45   $41.40  
  Purchase #4 $250.36   5.305%   $263.6416   $263.64   $263.65   $263.60  
  Purchase #5 $227.28   13.526%   $258.0219   $258.02   $258.00   $258.00  
  Purchase #6 $155.85   3.706%   $161.6258   $161.63   $161.65   $161.60  
  Purchase #7 $237.33   6.259%   $252.1845   $252.18   $252.20   $252.20  
  7 purchase totals = $1,044.30       $1,126.7451   $1,126.75   $1,126.80   $1,126.60