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 $60.78   10.236%   $67.0014   $67.00   $67.00   $67.00  
  Purchase #2 $113.74   7.565%   $122.3444   $122.34   $122.35   $122.30  
  Purchase #3 $140.36   3.723%   $145.5856   $145.59   $145.60   $145.60  
  Purchase #4 $119.43   4.843%   $125.214   $125.21   $125.20   $125.20  
  Purchase #5 $52.39   7.258%   $56.1925   $56.19   $56.20   $56.20  
  Purchase #6 $24.45   7.446%   $26.2705   $26.27   $26.25   $26.30  
  Purchase #7 $127.65   5.434%   $134.5865   $134.59   $134.60   $134.60  
  7 purchase totals = $638.80       $677.1949   $677.19   $677.20   $677.20