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 $192.59   4.533%   $201.3201   $201.32   $201.30   $201.30  
  Purchase #2 $191.44   5.337%   $201.6572   $201.66   $201.65   $201.70  
  Purchase #3 $58.98   8.446%   $63.9615   $63.96   $63.95   $64.00  
  Purchase #4 $183.80   6.131%   $195.0688   $195.07   $195.05   $195.10  
  Purchase #5 $121.87   5.770%   $128.9019   $128.90   $128.90   $128.90  
  Purchase #6 $33.25   3.646%   $34.4623   $34.46   $34.45   $34.50  
  Purchase #7 $142.34   5.815%   $150.6171   $150.62   $150.60   $150.60  
  7 purchase totals = $924.27       $975.9889   $975.99   $975.90   $976.10