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 $201.64   4.468%   $210.6493   $210.65   $210.65   $210.60  
  Purchase #2 $137.49   6.869%   $146.9342   $146.93   $146.95   $146.90  
  Purchase #3 $130.77   4.332%   $136.435   $136.44   $136.45   $136.40  
  Purchase #4 $228.81   13.822%   $260.4361   $260.44   $260.45   $260.40  
  Purchase #5 $54.99   5.507%   $58.0183   $58.02   $58.00   $58.00  
  Purchase #6 $137.44   7.243%   $147.3948   $147.39   $147.40   $147.40  
  Purchase #7 $221.34   5.544%   $233.6111   $233.61   $233.60   $233.60  
  7 purchase totals = $1,112.48       $1,193.4788   $1,193.48   $1,193.50   $1,193.30