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 $168.38   10.357%   $185.8191   $185.82   $185.80   $185.80  
  Purchase #2 $117.46   5.653%   $124.1   $124.10   $124.10   $124.10  
  Purchase #3 $208.78   7.678%   $224.8101   $224.81   $224.80   $224.80  
  Purchase #4 $218.90   4.714%   $229.2189   $229.22   $229.20   $229.20  
  Purchase #5 $96.44   10.208%   $106.2846   $106.28   $106.30   $106.30  
  Purchase #6 $87.74   7.630%   $94.4346   $94.43   $94.45   $94.40  
  Purchase #7 $42.88   8.843%   $46.6719   $46.67   $46.65   $46.70  
  7 purchase totals = $940.58       $1,011.3392   $1,011.33   $1,011.30   $1,011.30