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 $24.84   4.820%   $26.0373   $26.04   $26.05   $26.00  
  Purchase #2 $124.65   13.186%   $141.0863   $141.09   $141.10   $141.10  
  Purchase #3 $158.65   13.234%   $179.6457   $179.65   $179.65   $179.60  
  Purchase #4 $67.50   6.245%   $71.7154   $71.72   $71.70   $71.70  
  Purchase #5 $179.31   13.422%   $203.377   $203.38   $203.40   $203.40  
  Purchase #6 $143.81   8.605%   $156.1849   $156.18   $156.20   $156.20  
  Purchase #7 $65.59   12.331%   $73.6779   $73.68   $73.70   $73.70  
  7 purchase totals = $764.35       $851.7245   $851.74   $851.80   $851.70