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 $241.46   8.717%   $262.5081   $262.51   $262.50   $262.50  
  Purchase #2 $118.73   3.235%   $122.5709   $122.57   $122.55   $122.60  
  Purchase #3 $170.62   6.484%   $181.683   $181.68   $181.70   $181.70  
  Purchase #4 $44.88   12.423%   $50.4554   $50.46   $50.45   $50.50  
  Purchase #5 $90.58   7.120%   $97.0293   $97.03   $97.05   $97.00  
  Purchase #6 $61.72   3.361%   $63.7944   $63.79   $63.80   $63.80  
  Purchase #7 $79.45   5.159%   $83.5488   $83.55   $83.55   $83.50  
  7 purchase totals = $807.44       $861.5899   $861.59   $861.60   $861.60