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 $24.26   9.621%   $26.5941   $26.59   $26.60   $26.60  
  Purchase #2 $94.50   7.816%   $101.8861   $101.89   $101.90   $101.90  
  Purchase #3 $229.65   3.122%   $236.8197   $236.82   $236.80   $236.80  
  Purchase #4 $140.33   11.523%   $156.5002   $156.50   $156.50   $156.50  
  Purchase #5 $128.31   5.679%   $135.5967   $135.60   $135.60   $135.60  
  Purchase #6 $213.83   9.193%   $233.4874   $233.49   $233.50   $233.50  
  Purchase #7 $161.77   12.341%   $181.734   $181.73   $181.75   $181.70  
  7 purchase totals = $992.65       $1,072.6182   $1,072.62   $1,072.65   $1,072.60