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 $148.98   10.419%   $164.5022   $164.50   $164.50   $164.50  
  Purchase #2 $22.95   8.453%   $24.89   $24.89   $24.90   $24.90  
  Purchase #3 $35.38   5.691%   $37.3935   $37.39   $37.40   $37.40  
  Purchase #4 $118.46   3.218%   $122.272   $122.27   $122.25   $122.30  
  Purchase #5 $177.57   5.316%   $187.0096   $187.01   $187.00   $187.00  
  Purchase #6 $145.38   6.501%   $154.8312   $154.83   $154.85   $154.80  
  Purchase #7 $96.43   5.529%   $101.7616   $101.76   $101.75   $101.80  
  7 purchase totals = $745.15       $792.6601   $792.65   $792.65   $792.70