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 $183.93   4.420%   $192.0597   $192.06   $192.05   $192.10  
  Purchase #2 $216.49   8.212%   $234.2682   $234.27   $234.25   $234.30  
  Purchase #3 $58.46   6.335%   $62.1634   $62.16   $62.15   $62.20  
  Purchase #4 $69.79   9.616%   $76.501   $76.50   $76.50   $76.50  
  Purchase #5 $228.30   11.295%   $254.0865   $254.09   $254.10   $254.10  
  Purchase #6 $99.77   6.813%   $106.5673   $106.57   $106.55   $106.60  
  Purchase #7 $105.31   11.595%   $117.5207   $117.52   $117.50   $117.50  
  7 purchase totals = $962.05       $1,043.1668   $1,043.17   $1,043.10   $1,043.30