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 $112.29   10.638%   $124.2354   $124.24   $124.25   $124.20  
  Purchase #2 $169.28   4.239%   $176.4558   $176.46   $176.45   $176.50  
  Purchase #3 $175.90   4.695%   $184.1585   $184.16   $184.15   $184.20  
  Purchase #4 $244.84   8.568%   $265.8179   $265.82   $265.80   $265.80  
  Purchase #5 $112.31   12.553%   $126.4083   $126.41   $126.40   $126.40  
  Purchase #6 $51.77   10.609%   $57.2623   $57.26   $57.25   $57.30  
  Purchase #7 $117.52   7.295%   $126.0931   $126.09   $126.10   $126.10  
  7 purchase totals = $983.91       $1,060.4313   $1,060.44   $1,060.40   $1,060.50