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 $242.46   6.796%   $258.9376   $258.94   $258.95   $258.90  
  Purchase #2 $44.77   10.787%   $49.5993   $49.60   $49.60   $49.60  
  Purchase #3 $68.95   6.726%   $73.5876   $73.59   $73.60   $73.60  
  Purchase #4 $228.44   10.310%   $251.9922   $251.99   $252.00   $252.00  
  Purchase #5 $44.84   4.558%   $46.8838   $46.88   $46.90   $46.90  
  Purchase #6 $243.79   4.510%   $254.7849   $254.78   $254.80   $254.80  
  Purchase #7 $220.46   5.764%   $233.1673   $233.17   $233.15   $233.20  
  7 purchase totals = $1,093.71       $1,168.9527   $1,168.95   $1,169.00   $1,169.00