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 $41.88   6.253%   $44.4988   $44.50   $44.50   $44.50  
  Purchase #2 $227.39   5.638%   $240.2102   $240.21   $240.20   $240.20  
  Purchase #3 $82.26   9.523%   $90.0936   $90.09   $90.10   $90.10  
  Purchase #4 $217.97   7.392%   $234.0823   $234.08   $234.10   $234.10  
  Purchase #5 $114.92   3.268%   $118.6756   $118.68   $118.70   $118.70  
  Purchase #6 $56.32   9.651%   $61.7554   $61.76   $61.75   $61.80  
  Purchase #7 $240.76   7.245%   $258.2031   $258.20   $258.20   $258.20  
  7 purchase totals = $981.50       $1,047.5190   $1,047.52   $1,047.55   $1,047.60