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 $14.65   7.500%   $15.7488   $15.75   $15.75   $15.70  
  Purchase #2 $172.64   4.540%   $180.4779   $180.48   $180.50   $180.50  
  Purchase #3 $177.38   10.410%   $195.8453   $195.85   $195.85   $195.80  
  Purchase #4 $16.32   6.698%   $17.4131   $17.41   $17.40   $17.40  
  Purchase #5 $115.40   6.698%   $123.1295   $123.13   $123.15   $123.10  
  Purchase #6 $39.89   7.870%   $43.0293   $43.03   $43.05   $43.00  
  Purchase #7 $84.40   11.153%   $93.8131   $93.81   $93.80   $93.80  
  7 purchase totals = $620.68       $669.4570   $669.46   $669.50   $669.30