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 $204.26   12.743%   $230.2889   $230.29   $230.30   $230.30  
  Purchase #2 $155.68   12.778%   $175.5728   $175.57   $175.55   $175.60  
  Purchase #3 $52.75   6.581%   $56.2215   $56.22   $56.20   $56.20  
  Purchase #4 $164.38   13.281%   $186.2113   $186.21   $186.20   $186.20  
  Purchase #5 $105.30   12.575%   $118.5415   $118.54   $118.55   $118.50  
  Purchase #6 $104.41   6.381%   $111.0724   $111.07   $111.05   $111.10  
  Purchase #7 $203.64   12.253%   $228.592   $228.59   $228.60   $228.60  
  7 purchase totals = $990.42       $1,106.5004   $1,106.49   $1,106.45   $1,106.50