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 $213.57   9.470%   $233.7951   $233.80   $233.80   $233.80  
  Purchase #2 $68.28   13.565%   $77.5422   $77.54   $77.55   $77.50  
  Purchase #3 $49.86   13.656%   $56.6689   $56.67   $56.65   $56.70  
  Purchase #4 $249.37   6.106%   $264.5965   $264.60   $264.60   $264.60  
  Purchase #5 $234.63   6.649%   $250.2305   $250.23   $250.25   $250.20  
  Purchase #6 $147.84   11.643%   $165.053   $165.05   $165.05   $165.10  
  Purchase #7 $177.66   13.284%   $201.2604   $201.26   $201.25   $201.30  
  7 purchase totals = $1,141.21       $1,249.1466   $1,249.15   $1,249.15   $1,249.20