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 $89.90   9.665%   $98.5888   $98.59   $98.60   $98.60  
  Purchase #2 $132.92   6.608%   $141.7034   $141.70   $141.70   $141.70  
  Purchase #3 $23.76   12.612%   $26.7566   $26.76   $26.75   $26.80  
  Purchase #4 $222.65   7.194%   $238.6674   $238.67   $238.65   $238.70  
  Purchase #5 $216.90   5.516%   $228.8642   $228.86   $228.85   $228.90  
  Purchase #6 $182.93   13.612%   $207.8304   $207.83   $207.85   $207.80  
  Purchase #7 $6.59   13.159%   $7.4572   $7.46   $7.45   $7.50  
  7 purchase totals = $875.65       $949.8680   $949.87   $949.85   $950.00