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 $234.72   13.869%   $267.2733   $267.27   $267.25   $267.30  
  Purchase #2 $64.65   8.328%   $70.0341   $70.03   $70.05   $70.00  
  Purchase #3 $179.55   9.313%   $196.2715   $196.27   $196.25   $196.30  
  Purchase #4 $54.38   7.296%   $58.3476   $58.35   $58.35   $58.30  
  Purchase #5 $212.64   7.617%   $228.8368   $228.84   $228.85   $228.80  
  Purchase #6 $220.62   12.504%   $248.2063   $248.21   $248.20   $248.20  
  Purchase #7 $127.80   5.631%   $134.9964   $135.00   $135.00   $135.00  
  7 purchase totals = $1,094.36       $1,203.9660   $1,203.97   $1,203.95   $1,203.90