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 $235.58   8.188%   $254.8693   $254.87   $254.85   $254.90  
  Purchase #2 $73.31   8.577%   $79.5978   $79.60   $79.60   $79.60  
  Purchase #3 $174.77   4.802%   $183.1625   $183.16   $183.15   $183.20  
  Purchase #4 $41.54   10.411%   $45.8647   $45.86   $45.85   $45.90  
  Purchase #5 $234.57   3.451%   $242.665   $242.67   $242.65   $242.70  
  Purchase #6 $15.44   10.363%   $17.04   $17.04   $17.05   $17.00  
  Purchase #7 $143.85   6.642%   $153.4045   $153.40   $153.40   $153.40  
  7 purchase totals = $919.06       $976.6038   $976.60   $976.55   $976.70