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 $38.45   12.695%   $43.3312   $43.33   $43.35   $43.30  
  Purchase #2 $165.74   12.599%   $186.6216   $186.62   $186.60   $186.60  
  Purchase #3 $54.25   13.324%   $61.4783   $61.48   $61.50   $61.50  
  Purchase #4 $32.99   5.155%   $34.6906   $34.69   $34.70   $34.70  
  Purchase #5 $173.36   9.319%   $189.5154   $189.52   $189.50   $189.50  
  Purchase #6 $193.41   7.110%   $207.1615   $207.16   $207.15   $207.20  
  Purchase #7 $64.64   13.508%   $73.3716   $73.37   $73.35   $73.40  
  7 purchase totals = $722.84       $796.1702   $796.17   $796.15   $796.20