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 $43.89   4.763%   $45.9805   $45.98   $46.00   $46.00  
  Purchase #2 $19.41   6.289%   $20.6307   $20.63   $20.65   $20.60  
  Purchase #3 $75.51   5.509%   $79.6698   $79.67   $79.65   $79.70  
  Purchase #4 $48.38   7.783%   $52.1454   $52.15   $52.15   $52.10  
  Purchase #5 $200.52   3.470%   $207.478   $207.48   $207.50   $207.50  
  Purchase #6 $142.59   12.596%   $160.5506   $160.55   $160.55   $160.60  
  Purchase #7 $213.33   9.438%   $233.4641   $233.46   $233.45   $233.50  
  7 purchase totals = $743.63       $799.9191   $799.92   $799.95   $800.00