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 $238.70   9.821%   $262.1427   $262.14   $262.15   $262.10  
  Purchase #2 $171.43   12.317%   $192.545   $192.55   $192.55   $192.50  
  Purchase #3 $92.51   11.197%   $102.8683   $102.87   $102.85   $102.90  
  Purchase #4 $187.98   9.425%   $205.6971   $205.70   $205.70   $205.70  
  Purchase #5 $11.68   7.591%   $12.5666   $12.57   $12.55   $12.60  
  Purchase #6 $54.31   4.643%   $56.8316   $56.83   $56.85   $56.80  
  Purchase #7 $70.80   7.563%   $76.1546   $76.15   $76.15   $76.20  
  7 purchase totals = $827.41       $908.8059   $908.81   $908.80   $908.80