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 $242.96   10.821%   $269.2507   $269.25   $269.25   $269.30  
  Purchase #2 $42.86   11.198%   $47.6595   $47.66   $47.65   $47.70  
  Purchase #3 $57.46   10.507%   $63.4973   $63.50   $63.50   $63.50  
  Purchase #4 $163.29   12.168%   $183.1591   $183.16   $183.15   $183.20  
  Purchase #5 $169.58   9.790%   $186.1819   $186.18   $186.20   $186.20  
  Purchase #6 $142.78   5.440%   $150.5472   $150.55   $150.55   $150.50  
  Purchase #7 $232.42   9.155%   $253.6981   $253.70   $253.70   $253.70  
  7 purchase totals = $1,051.35       $1,153.9938   $1,154.00   $1,154.00   $1,154.10