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 $58.59   3.218%   $60.4754   $60.48   $60.50   $60.50  
  Purchase #2 $221.72   11.602%   $247.444   $247.44   $247.45   $247.40  
  Purchase #3 $66.93   6.115%   $71.0228   $71.02   $71.00   $71.00  
  Purchase #4 $108.55   4.569%   $113.5096   $113.51   $113.50   $113.50  
  Purchase #5 $181.65   6.200%   $192.9123   $192.91   $192.90   $192.90  
  Purchase #6 $161.66   8.449%   $175.3187   $175.32   $175.30   $175.30  
  Purchase #7 $220.67   5.158%   $232.0522   $232.05   $232.05   $232.10  
  7 purchase totals = $1,019.77       $1,092.7350   $1,092.73   $1,092.70   $1,092.70