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 $164.65   13.269%   $186.4974   $186.50   $186.50   $186.50  
  Purchase #2 $25.41   6.758%   $27.1272   $27.13   $27.15   $27.10  
  Purchase #3 $163.49   7.820%   $176.2749   $176.27   $176.25   $176.30  
  Purchase #4 $153.66   7.149%   $164.6452   $164.65   $164.65   $164.60  
  Purchase #5 $34.32   7.176%   $36.7828   $36.78   $36.80   $36.80  
  Purchase #6 $11.54   6.299%   $12.2669   $12.27   $12.25   $12.30  
  Purchase #7 $145.99   13.650%   $165.9176   $165.92   $165.90   $165.90  
  7 purchase totals = $699.06       $769.5120   $769.52   $769.50   $769.50