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 $82.77   3.874%   $85.9765   $85.98   $86.00   $86.00  
  Purchase #2 $155.93   11.230%   $173.4409   $173.44   $173.45   $173.40  
  Purchase #3 $135.84   8.721%   $147.6866   $147.69   $147.70   $147.70  
  Purchase #4 $225.90   10.666%   $249.9945   $249.99   $250.00   $250.00  
  Purchase #5 $244.89   4.786%   $256.6104   $256.61   $256.60   $256.60  
  Purchase #6 $45.96   3.838%   $47.7239   $47.72   $47.70   $47.70  
  Purchase #7 $37.47   6.597%   $39.9419   $39.94   $39.95   $39.90  
  7 purchase totals = $928.76       $1,001.3747   $1,001.37   $1,001.40   $1,001.30