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 $62.69   5.418%   $66.0865   $66.09   $66.10   $66.10  
  Purchase #2 $161.44   5.566%   $170.4258   $170.43   $170.45   $170.40  
  Purchase #3 $208.70   5.672%   $220.5375   $220.54   $220.55   $220.50  
  Purchase #4 $147.62   13.592%   $167.6845   $167.68   $167.70   $167.70  
  Purchase #5 $6.65   10.138%   $7.3242   $7.32   $7.30   $7.30  
  Purchase #6 $231.62   6.845%   $247.4744   $247.47   $247.45   $247.50  
  Purchase #7 $55.35   10.858%   $61.3599   $61.36   $61.35   $61.40  
  7 purchase totals = $874.07       $940.8928   $940.89   $940.90   $940.90