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 $74.60   13.279%   $84.5061   $84.51   $84.50   $84.50  
  Purchase #2 $136.26   11.604%   $152.0716   $152.07   $152.05   $152.10  
  Purchase #3 $60.51   9.486%   $66.25   $66.25   $66.25   $66.30  
  Purchase #4 $65.42   9.476%   $71.6192   $71.62   $71.60   $71.60  
  Purchase #5 $232.69   4.828%   $243.9243   $243.92   $243.90   $243.90  
  Purchase #6 $54.28   6.617%   $57.8717   $57.87   $57.85   $57.90  
  Purchase #7 $74.95   6.325%   $79.6906   $79.69   $79.70   $79.70  
  7 purchase totals = $698.71       $755.9335   $755.93   $755.85   $756.00