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 $42.34   3.268%   $43.7237   $43.72   $43.70   $43.70  
  Purchase #2 $117.48   7.108%   $125.8305   $125.83   $125.85   $125.80  
  Purchase #3 $76.75   6.165%   $81.4816   $81.48   $81.50   $81.50  
  Purchase #4 $121.83   10.359%   $134.4504   $134.45   $134.45   $134.50  
  Purchase #5 $111.33   6.235%   $118.2714   $118.27   $118.25   $118.30  
  Purchase #6 $243.27   8.726%   $264.4977   $264.50   $264.50   $264.50  
  Purchase #7 $24.65   11.505%   $27.486   $27.49   $27.50   $27.50  
  7 purchase totals = $737.65       $795.7413   $795.74   $795.75   $795.80