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 $206.98   12.102%   $232.0287   $232.03   $232.05   $232.00  
  Purchase #2 $27.72   5.642%   $29.284   $29.28   $29.30   $29.30  
  Purchase #3 $228.70   10.565%   $252.8622   $252.86   $252.85   $252.90  
  Purchase #4 $100.72   5.763%   $106.5245   $106.52   $106.50   $106.50  
  Purchase #5 $168.98   10.165%   $186.1568   $186.16   $186.15   $186.20  
  Purchase #6 $214.77   3.834%   $223.0043   $223.00   $223.00   $223.00  
  Purchase #7 $139.50   6.348%   $148.3555   $148.36   $148.35   $148.40  
  7 purchase totals = $1,087.37       $1,178.2160   $1,178.21   $1,178.20   $1,178.30