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 $243.56   13.724%   $276.9862   $276.99   $277.00   $277.00  
  Purchase #2 $86.87   5.430%   $91.587   $91.59   $91.60   $91.60  
  Purchase #3 $233.88   13.730%   $265.9917   $265.99   $266.00   $266.00  
  Purchase #4 $172.35   11.365%   $191.9376   $191.94   $191.95   $191.90  
  Purchase #5 $182.94   9.566%   $200.44   $200.44   $200.45   $200.40  
  Purchase #6 $78.53   8.309%   $85.0551   $85.06   $85.05   $85.10  
  Purchase #7 $83.73   8.430%   $90.7884   $90.79   $90.80   $90.80  
  7 purchase totals = $1,081.86       $1,202.7860   $1,202.80   $1,202.85   $1,202.80