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 $232.84   7.652%   $250.6569   $250.66   $250.65   $250.70  
  Purchase #2 $178.73   9.691%   $196.0507   $196.05   $196.05   $196.10  
  Purchase #3 $46.67   12.616%   $52.5579   $52.56   $52.55   $52.60  
  Purchase #4 $76.78   4.812%   $80.4747   $80.47   $80.45   $80.50  
  Purchase #5 $220.29   11.733%   $246.1366   $246.14   $246.15   $246.10  
  Purchase #6 $83.64   3.126%   $86.2546   $86.25   $86.25   $86.30  
  Purchase #7 $113.92   5.681%   $120.3918   $120.39   $120.40   $120.40  
  7 purchase totals = $952.87       $1,032.5232   $1,032.52   $1,032.50   $1,032.70