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 $243.41   8.750%   $264.7084   $264.71   $264.70   $264.70  
  Purchase #2 $104.72   8.684%   $113.8139   $113.81   $113.80   $113.80  
  Purchase #3 $64.77   7.148%   $69.3998   $69.40   $69.40   $69.40  
  Purchase #4 $134.33   7.539%   $144.4571   $144.46   $144.45   $144.50  
  Purchase #5 $195.42   7.305%   $209.6954   $209.70   $209.70   $209.70  
  Purchase #6 $138.26   7.215%   $148.2355   $148.24   $148.25   $148.20  
  Purchase #7 $89.45   7.392%   $96.0621   $96.06   $96.05   $96.10  
  7 purchase totals = $970.36       $1,046.3722   $1,046.38   $1,046.35   $1,046.40