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 $24.77   7.598%   $26.652   $26.65   $26.65   $26.70  
  Purchase #2 $243.90   11.193%   $271.1997   $271.20   $271.20   $271.20  
  Purchase #3 $10.70   10.647%   $11.8392   $11.84   $11.85   $11.80  
  Purchase #4 $196.95   13.520%   $223.5776   $223.58   $223.60   $223.60  
  Purchase #5 $243.41   4.522%   $254.417   $254.42   $254.40   $254.40  
  Purchase #6 $5.62   5.366%   $5.9216   $5.92   $5.90   $5.90  
  Purchase #7 $150.48   6.767%   $160.663   $160.66   $160.65   $160.70  
  7 purchase totals = $875.83       $954.2701   $954.27   $954.25   $954.30