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 $55.42   5.110%   $58.252   $58.25   $58.25   $58.30  
  Purchase #2 $24.72   6.496%   $26.3258   $26.33   $26.35   $26.30  
  Purchase #3 $246.25   10.838%   $272.9386   $272.94   $272.95   $272.90  
  Purchase #4 $170.42   13.339%   $193.1523   $193.15   $193.15   $193.20  
  Purchase #5 $95.75   8.562%   $103.9481   $103.95   $103.95   $103.90  
  Purchase #6 $220.41   12.774%   $248.5652   $248.57   $248.55   $248.60  
  Purchase #7 $206.28   10.507%   $227.9538   $227.95   $227.95   $228.00  
  7 purchase totals = $1,019.25       $1,131.1358   $1,131.14   $1,131.15   $1,131.20