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 $140.27   11.239%   $156.0349   $156.03   $156.05   $156.00  
  Purchase #2 $44.75   7.321%   $48.0261   $48.03   $48.05   $48.00  
  Purchase #3 $229.69   5.614%   $242.5848   $242.58   $242.60   $242.60  
  Purchase #4 $215.74   11.317%   $240.1553   $240.16   $240.15   $240.20  
  Purchase #5 $237.54   5.352%   $250.2531   $250.25   $250.25   $250.30  
  Purchase #6 $14.35   7.718%   $15.4575   $15.46   $15.45   $15.50  
  Purchase #7 $67.42   4.599%   $70.5206   $70.52   $70.50   $70.50  
  7 purchase totals = $949.76       $1,023.0323   $1,023.03   $1,023.05   $1,023.10