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 $154.77   4.417%   $161.6062   $161.61   $161.60   $161.60  
  Purchase #2 $232.41   9.705%   $254.9654   $254.97   $254.95   $255.00  
  Purchase #3 $74.97   8.855%   $81.6086   $81.61   $81.60   $81.60  
  Purchase #4 $238.82   8.785%   $259.8003   $259.80   $259.80   $259.80  
  Purchase #5 $188.42   6.656%   $200.9612   $200.96   $200.95   $201.00  
  Purchase #6 $180.87   5.207%   $190.2879   $190.29   $190.30   $190.30  
  Purchase #7 $25.38   3.328%   $26.2246   $26.22   $26.20   $26.20  
  7 purchase totals = $1,095.64       $1,175.4542   $1,175.46   $1,175.40   $1,175.50