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 $153.87   8.830%   $167.4567   $167.46   $167.45   $167.50  
  Purchase #2 $217.93   7.812%   $234.9547   $234.95   $234.95   $235.00  
  Purchase #3 $203.50   12.186%   $228.2985   $228.30   $228.30   $228.30  
  Purchase #4 $58.54   4.825%   $61.3646   $61.36   $61.35   $61.40  
  Purchase #5 $247.65   11.541%   $276.2313   $276.23   $276.25   $276.20  
  Purchase #6 $100.38   5.133%   $105.5325   $105.53   $105.55   $105.50  
  Purchase #7 $26.88   8.838%   $29.2557   $29.26   $29.25   $29.30  
  7 purchase totals = $1,008.75       $1,103.0940   $1,103.09   $1,103.10   $1,103.20