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 $62.25   13.812%   $70.848   $70.85   $70.85   $70.80  
  Purchase #2 $170.29   10.855%   $188.775   $188.78   $188.80   $188.80  
  Purchase #3 $113.56   7.666%   $122.2655   $122.27   $122.25   $122.30  
  Purchase #4 $123.99   3.182%   $127.9354   $127.94   $127.95   $127.90  
  Purchase #5 $147.93   9.727%   $162.3192   $162.32   $162.30   $162.30  
  Purchase #6 $105.76   9.417%   $115.7194   $115.72   $115.70   $115.70  
  Purchase #7 $229.35   11.226%   $255.0968   $255.10   $255.10   $255.10  
  7 purchase totals = $953.13       $1,042.9593   $1,042.98   $1,042.95   $1,042.90