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 $179.42   12.782%   $202.3535   $202.35   $202.35   $202.40  
  Purchase #2 $199.68   13.584%   $226.8045   $226.80   $226.80   $226.80  
  Purchase #3 $83.35   3.155%   $85.9797   $85.98   $86.00   $86.00  
  Purchase #4 $214.46   7.810%   $231.2093   $231.21   $231.20   $231.20  
  Purchase #5 $237.28   5.438%   $250.1833   $250.18   $250.20   $250.20  
  Purchase #6 $163.82   10.791%   $181.4978   $181.50   $181.50   $181.50  
  Purchase #7 $34.81   9.842%   $38.236   $38.24   $38.25   $38.20  
  7 purchase totals = $1,112.82       $1,216.2641   $1,216.26   $1,216.30   $1,216.30