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 $58.93   13.465%   $66.8649   $66.86   $66.85   $66.90  
  Purchase #2 $66.73   3.659%   $69.1717   $69.17   $69.15   $69.20  
  Purchase #3 $218.40   7.646%   $235.0989   $235.10   $235.10   $235.10  
  Purchase #4 $23.69   10.664%   $26.2163   $26.22   $26.20   $26.20  
  Purchase #5 $80.83   13.207%   $91.5052   $91.51   $91.50   $91.50  
  Purchase #6 $168.97   11.705%   $188.7479   $188.75   $188.75   $188.70  
  Purchase #7 $150.43   3.832%   $156.1945   $156.19   $156.20   $156.20  
  7 purchase totals = $767.98       $833.7994   $833.80   $833.75   $833.80