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 $70.41   9.719%   $77.2531   $77.25   $77.25   $77.30  
  Purchase #2 $55.93   12.119%   $62.7082   $62.71   $62.70   $62.70  
  Purchase #3 $77.72   10.224%   $85.6661   $85.67   $85.65   $85.70  
  Purchase #4 $178.27   8.294%   $193.0557   $193.06   $193.05   $193.10  
  Purchase #5 $169.89   10.353%   $187.4787   $187.48   $187.50   $187.50  
  Purchase #6 $187.36   9.499%   $205.1573   $205.16   $205.15   $205.20  
  Purchase #7 $192.86   7.115%   $206.582   $206.58   $206.60   $206.60  
  7 purchase totals = $932.44       $1,017.9011   $1,017.91   $1,017.90   $1,018.10