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 $204.25   13.660%   $232.1506   $232.15   $232.15   $232.20  
  Purchase #2 $219.54   4.792%   $230.0604   $230.06   $230.05   $230.10  
  Purchase #3 $11.33   12.266%   $12.7197   $12.72   $12.70   $12.70  
  Purchase #4 $221.33   8.696%   $240.5769   $240.58   $240.60   $240.60  
  Purchase #5 $207.42   8.660%   $225.3826   $225.38   $225.40   $225.40  
  Purchase #6 $225.26   11.732%   $251.6875   $251.69   $251.70   $251.70  
  Purchase #7 $32.51   10.723%   $35.996   $36.00   $36.00   $36.00  
  7 purchase totals = $1,121.64       $1,228.5737   $1,228.58   $1,228.60   $1,228.70