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 $208.27   12.851%   $235.0348   $235.03   $235.05   $235.00  
  Purchase #2 $242.28   3.297%   $250.268   $250.27   $250.25   $250.30  
  Purchase #3 $58.50   8.721%   $63.6018   $63.60   $63.60   $63.60  
  Purchase #4 $179.65   6.582%   $191.4746   $191.47   $191.45   $191.50  
  Purchase #5 $77.41   7.763%   $83.4193   $83.42   $83.40   $83.40  
  Purchase #6 $115.25   7.174%   $123.518   $123.52   $123.50   $123.50  
  Purchase #7 $39.70   11.691%   $44.3413   $44.34   $44.35   $44.30  
  7 purchase totals = $921.06       $991.6578   $991.65   $991.60   $991.60