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 $183.55   13.300%   $207.9622   $207.96   $207.95   $208.00  
  Purchase #2 $228.62   9.736%   $250.8784   $250.88   $250.90   $250.90  
  Purchase #3 $161.92   10.518%   $178.9507   $178.95   $178.95   $179.00  
  Purchase #4 $54.84   8.615%   $59.5645   $59.56   $59.55   $59.60  
  Purchase #5 $211.97   7.847%   $228.6033   $228.60   $228.60   $228.60  
  Purchase #6 $185.37   10.255%   $204.3797   $204.38   $204.40   $204.40  
  Purchase #7 $68.56   6.787%   $73.2132   $73.21   $73.20   $73.20  
  7 purchase totals = $1,094.83       $1,203.5520   $1,203.54   $1,203.55   $1,203.70