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 $84.38   13.836%   $96.0548   $96.05   $96.05   $96.10  
  Purchase #2 $211.54   12.805%   $238.6277   $238.63   $238.65   $238.60  
  Purchase #3 $7.86   8.704%   $8.5441   $8.54   $8.55   $8.50  
  Purchase #4 $243.39   11.202%   $270.6545   $270.65   $270.65   $270.70  
  Purchase #5 $160.63   13.855%   $182.8853   $182.89   $182.90   $182.90  
  Purchase #6 $150.42   3.870%   $156.2413   $156.24   $156.25   $156.20  
  Purchase #7 $159.35   10.190%   $175.5878   $175.59   $175.60   $175.60  
  7 purchase totals = $1,017.57       $1,128.5955   $1,128.59   $1,128.65   $1,128.60