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 $202.84   5.807%   $214.6189   $214.62   $214.60   $214.60  
  Purchase #2 $57.39   6.727%   $61.2506   $61.25   $61.25   $61.30  
  Purchase #3 $29.80   4.655%   $31.1872   $31.19   $31.20   $31.20  
  Purchase #4 $211.54   13.575%   $240.2566   $240.26   $240.25   $240.30  
  Purchase #5 $72.29   11.533%   $80.6272   $80.63   $80.65   $80.60  
  Purchase #6 $155.74   12.721%   $175.5517   $175.55   $175.55   $175.60  
  Purchase #7 $182.85   9.771%   $200.7163   $200.72   $200.70   $200.70  
  7 purchase totals = $912.45       $1,004.2085   $1,004.22   $1,004.20   $1,004.30