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 $91.69   13.676%   $104.2295   $104.23   $104.25   $104.20  
  Purchase #2 $181.65   10.294%   $200.3491   $200.35   $200.35   $200.30  
  Purchase #3 $102.57   10.600%   $113.4424   $113.44   $113.45   $113.40  
  Purchase #4 $174.74   6.552%   $186.189   $186.19   $186.20   $186.20  
  Purchase #5 $64.44   8.227%   $69.7415   $69.74   $69.75   $69.70  
  Purchase #6 $218.66   5.212%   $230.0566   $230.06   $230.05   $230.10  
  Purchase #7 $115.90   5.685%   $122.4889   $122.49   $122.50   $122.50  
  7 purchase totals = $949.65       $1,026.4970   $1,026.50   $1,026.55   $1,026.40