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 $68.63   10.399%   $75.7668   $75.77   $75.75   $75.80  
  Purchase #2 $13.31   5.670%   $14.0647   $14.06   $14.05   $14.10  
  Purchase #3 $12.40   4.212%   $12.9223   $12.92   $12.90   $12.90  
  Purchase #4 $58.85   5.809%   $62.2686   $62.27   $62.25   $62.30  
  Purchase #5 $9.39   12.624%   $10.5754   $10.58   $10.60   $10.60  
  Purchase #6 $111.44   10.298%   $122.9161   $122.92   $122.90   $122.90  
  Purchase #7 $49.44   12.801%   $55.7688   $55.77   $55.75   $55.80  
  7 purchase totals = $323.46       $354.2827   $354.29   $354.20   $354.40