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 $248.35   8.601%   $269.7106   $269.71   $269.70   $269.70  
  Purchase #2 $104.67   8.666%   $113.7407   $113.74   $113.75   $113.70  
  Purchase #3 $87.92   13.197%   $99.5228   $99.52   $99.50   $99.50  
  Purchase #4 $182.98   5.619%   $193.2616   $193.26   $193.25   $193.30  
  Purchase #5 $71.90   12.589%   $80.9515   $80.95   $80.95   $81.00  
  Purchase #6 $162.38   8.462%   $176.1206   $176.12   $176.10   $176.10  
  Purchase #7 $56.77   8.395%   $61.5358   $61.54   $61.55   $61.50  
  7 purchase totals = $914.97       $994.8436   $994.84   $994.80   $994.80