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 $234.50   13.411%   $265.9488   $265.95   $265.95   $265.90  
  Purchase #2 $23.37   6.276%   $24.8367   $24.84   $24.85   $24.80  
  Purchase #3 $215.93   3.776%   $224.0835   $224.08   $224.10   $224.10  
  Purchase #4 $114.93   9.809%   $126.2035   $126.20   $126.20   $126.20  
  Purchase #5 $228.50   11.682%   $255.1934   $255.19   $255.20   $255.20  
  Purchase #6 $234.57   11.636%   $261.8646   $261.86   $261.85   $261.90  
  Purchase #7 $8.37   11.289%   $9.3149   $9.31   $9.30   $9.30  
  7 purchase totals = $1,060.17       $1,167.4454   $1,167.43   $1,167.45   $1,167.40