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 $154.31   8.379%   $167.2396   $167.24   $167.25   $167.20  
  Purchase #2 $110.83   8.824%   $120.6096   $120.61   $120.60   $120.60  
  Purchase #3 $25.87   8.347%   $28.0294   $28.03   $28.05   $28.00  
  Purchase #4 $250.57   13.266%   $283.8106   $283.81   $283.80   $283.80  
  Purchase #5 $218.97   8.856%   $238.362   $238.36   $238.35   $238.40  
  Purchase #6 $54.41   3.502%   $56.3154   $56.32   $56.30   $56.30  
  Purchase #7 $214.56   4.532%   $224.2839   $224.28   $224.30   $224.30  
  7 purchase totals = $1,029.52       $1,118.6505   $1,118.65   $1,118.65   $1,118.60