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 $247.33   10.494%   $273.2848   $273.28   $273.30   $273.30  
  Purchase #2 $56.67   6.235%   $60.2034   $60.20   $60.20   $60.20  
  Purchase #3 $102.61   11.752%   $114.6687   $114.67   $114.65   $114.70  
  Purchase #4 $34.89   3.183%   $36.0005   $36.00   $36.00   $36.00  
  Purchase #5 $143.77   3.820%   $149.262   $149.26   $149.25   $149.30  
  Purchase #6 $145.29   6.403%   $154.5929   $154.59   $154.60   $154.60  
  Purchase #7 $115.67   6.656%   $123.369   $123.37   $123.35   $123.40  
  7 purchase totals = $846.23       $911.3813   $911.37   $911.35   $911.50