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 $23.48   13.373%   $26.62   $26.62   $26.60   $26.60  
  Purchase #2 $72.86   11.655%   $81.3518   $81.35   $81.35   $81.40  
  Purchase #3 $188.54   5.118%   $198.1895   $198.19   $198.20   $198.20  
  Purchase #4 $74.47   11.870%   $83.3096   $83.31   $83.30   $83.30  
  Purchase #5 $41.49   12.622%   $46.7269   $46.73   $46.75   $46.70  
  Purchase #6 $98.66   6.430%   $105.0038   $105.00   $105.00   $105.00  
  Purchase #7 $196.36   6.677%   $209.471   $209.47   $209.45   $209.50  
  7 purchase totals = $695.86       $750.6726   $750.67   $750.65   $750.70