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 $81.46   3.253%   $84.1099   $84.11   $84.10   $84.10  
  Purchase #2 $204.46   11.789%   $228.5638   $228.56   $228.55   $228.60  
  Purchase #3 $58.59   5.692%   $61.9249   $61.92   $61.90   $61.90  
  Purchase #4 $194.38   7.554%   $209.0635   $209.06   $209.05   $209.10  
  Purchase #5 $182.62   7.867%   $196.9867   $196.99   $197.00   $197.00  
  Purchase #6 $234.66   13.149%   $265.5154   $265.52   $265.50   $265.50  
  Purchase #7 $40.88   5.714%   $43.2159   $43.22   $43.20   $43.20  
  7 purchase totals = $997.05       $1,089.3801   $1,089.38   $1,089.30   $1,089.40