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   7.247%   $26.6402   $26.64   $26.65   $26.60  
  Purchase #2 $212.82   8.519%   $230.9501   $230.95   $230.95   $231.00  
  Purchase #3 $105.97   7.436%   $113.8499   $113.85   $113.85   $113.80  
  Purchase #4 $38.61   6.691%   $41.1934   $41.19   $41.20   $41.20  
  Purchase #5 $201.31   11.476%   $224.4123   $224.41   $224.40   $224.40  
  Purchase #6 $95.38   4.132%   $99.3211   $99.32   $99.30   $99.30  
  Purchase #7 $107.71   13.723%   $122.491   $122.49   $122.50   $122.50  
  7 purchase totals = $786.64       $858.8580   $858.85   $858.85   $858.80