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 $232.97   10.112%   $256.5279   $256.53   $256.55   $256.50  
  Purchase #2 $60.75   9.581%   $66.5705   $66.57   $66.55   $66.60  
  Purchase #3 $135.74   5.740%   $143.5315   $143.53   $143.55   $143.50  
  Purchase #4 $218.61   10.511%   $241.5881   $241.59   $241.60   $241.60  
  Purchase #5 $58.42   6.796%   $62.3902   $62.39   $62.40   $62.40  
  Purchase #6 $214.40   8.164%   $231.9036   $231.90   $231.90   $231.90  
  Purchase #7 $211.36   12.639%   $238.0738   $238.07   $238.05   $238.10  
  7 purchase totals = $1,132.25       $1,240.5856   $1,240.58   $1,240.60   $1,240.60