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 $237.64   6.331%   $252.685   $252.69   $252.70   $252.70  
  Purchase #2 $38.35   3.759%   $39.7916   $39.79   $39.80   $39.80  
  Purchase #3 $140.43   11.610%   $156.7339   $156.73   $156.75   $156.70  
  Purchase #4 $192.51   4.822%   $201.7928   $201.79   $201.80   $201.80  
  Purchase #5 $58.44   13.631%   $66.406   $66.41   $66.40   $66.40  
  Purchase #6 $171.44   7.275%   $183.9123   $183.91   $183.90   $183.90  
  Purchase #7 $119.91   11.459%   $133.6505   $133.65   $133.65   $133.70  
  7 purchase totals = $958.72       $1,034.9721   $1,034.97   $1,035.00   $1,035.00