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 $188.29   4.791%   $197.311   $197.31   $197.30   $197.30  
  Purchase #2 $241.57   13.279%   $273.6481   $273.65   $273.65   $273.60  
  Purchase #3 $164.56   6.159%   $174.6953   $174.70   $174.70   $174.70  
  Purchase #4 $214.37   6.708%   $228.7499   $228.75   $228.75   $228.70  
  Purchase #5 $59.32   12.709%   $66.859   $66.86   $66.85   $66.90  
  Purchase #6 $5.70   6.135%   $6.0497   $6.05   $6.05   $6.00  
  Purchase #7 $51.49   10.833%   $57.0679   $57.07   $57.05   $57.10  
  7 purchase totals = $925.30       $1,004.3809   $1,004.39   $1,004.35   $1,004.30