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 $48.78   13.693%   $55.4594   $55.46   $55.45   $55.50  
  Purchase #2 $153.76   5.657%   $162.4582   $162.46   $162.45   $162.50  
  Purchase #3 $149.26   11.830%   $166.9175   $166.92   $166.90   $166.90  
  Purchase #4 $180.58   12.864%   $203.8098   $203.81   $203.80   $203.80  
  Purchase #5 $242.71   4.149%   $252.78   $252.78   $252.80   $252.80  
  Purchase #6 $10.45   12.155%   $11.7202   $11.72   $11.70   $11.70  
  Purchase #7 $145.70   10.786%   $161.4152   $161.42   $161.40   $161.40  
  7 purchase totals = $931.24       $1,014.5603   $1,014.57   $1,014.50   $1,014.60