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 $88.87   8.315%   $96.2595   $96.26   $96.25   $96.30  
  Purchase #2 $179.31   6.647%   $191.2287   $191.23   $191.25   $191.20  
  Purchase #3 $208.26   6.588%   $221.9802   $221.98   $222.00   $222.00  
  Purchase #4 $111.36   6.761%   $118.889   $118.89   $118.90   $118.90  
  Purchase #5 $125.88   11.256%   $140.0491   $140.05   $140.05   $140.00  
  Purchase #6 $39.67   3.505%   $41.0604   $41.06   $41.05   $41.10  
  Purchase #7 $167.38   13.824%   $190.5186   $190.52   $190.50   $190.50  
  7 purchase totals = $920.73       $999.9855   $999.99   $1,000.00   $1,000.00