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 $24.93   6.543%   $26.5612   $26.56   $26.55   $26.60  
  Purchase #2 $78.35   13.194%   $88.6875   $88.69   $88.70   $88.70  
  Purchase #3 $46.28   8.452%   $50.1916   $50.19   $50.20   $50.20  
  Purchase #4 $237.43   7.747%   $255.8237   $255.82   $255.80   $255.80  
  Purchase #5 $170.79   6.530%   $181.9426   $181.94   $181.95   $181.90  
  Purchase #6 $157.26   9.112%   $171.5895   $171.59   $171.60   $171.60  
  Purchase #7 $147.29   9.452%   $161.2119   $161.21   $161.20   $161.20  
  7 purchase totals = $862.33       $936.0080   $936.00   $936.00   $936.00