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 $25.31   5.591%   $26.7251   $26.73   $26.75   $26.70  
  Purchase #2 $228.71   8.807%   $248.8525   $248.85   $248.85   $248.90  
  Purchase #3 $93.84   13.783%   $106.774   $106.77   $106.75   $106.80  
  Purchase #4 $23.75   13.751%   $27.0159   $27.02   $27.00   $27.00  
  Purchase #5 $239.86   6.738%   $256.0218   $256.02   $256.00   $256.00  
  Purchase #6 $86.29   6.336%   $91.7573   $91.76   $91.75   $91.80  
  Purchase #7 $161.40   6.534%   $171.9459   $171.95   $171.95   $171.90  
  7 purchase totals = $859.16       $929.0925   $929.10   $929.05   $929.10