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 $52.44   7.456%   $56.3499   $56.35   $56.35   $56.30  
  Purchase #2 $193.31   8.783%   $210.2884   $210.29   $210.30   $210.30  
  Purchase #3 $167.59   6.692%   $178.8051   $178.81   $178.80   $178.80  
  Purchase #4 $100.63   3.577%   $104.2295   $104.23   $104.25   $104.20  
  Purchase #5 $201.58   7.505%   $216.7086   $216.71   $216.70   $216.70  
  Purchase #6 $52.73   6.242%   $56.0214   $56.02   $56.00   $56.00  
  Purchase #7 $71.41   6.850%   $76.3016   $76.30   $76.30   $76.30  
  7 purchase totals = $839.69       $898.7045   $898.71   $898.70   $898.60