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 $238.70   10.656%   $264.1359   $264.14   $264.15   $264.10  
  Purchase #2 $247.67   4.716%   $259.3501   $259.35   $259.35   $259.40  
  Purchase #3 $173.95   11.551%   $194.043   $194.04   $194.05   $194.00  
  Purchase #4 $57.37   11.576%   $64.0112   $64.01   $64.00   $64.00  
  Purchase #5 $48.95   7.424%   $52.584   $52.58   $52.60   $52.60  
  Purchase #6 $229.35   12.637%   $258.333   $258.33   $258.35   $258.30  
  Purchase #7 $37.56   3.137%   $38.7383   $38.74   $38.75   $38.70  
  7 purchase totals = $1,033.55       $1,131.1955   $1,131.19   $1,131.25   $1,131.10