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 $88.34   7.149%   $94.6554   $94.66   $94.65   $94.70  
  Purchase #2 $237.71   10.698%   $263.1402   $263.14   $263.15   $263.10  
  Purchase #3 $234.94   12.845%   $265.118   $265.12   $265.10   $265.10  
  Purchase #4 $95.85   13.307%   $108.6048   $108.60   $108.60   $108.60  
  Purchase #5 $180.28   12.822%   $203.3955   $203.40   $203.40   $203.40  
  Purchase #6 $9.81   6.526%   $10.4502   $10.45   $10.45   $10.50  
  Purchase #7 $222.63   12.728%   $250.9663   $250.97   $250.95   $251.00  
  7 purchase totals = $1,069.56       $1,196.3304   $1,196.34   $1,196.30   $1,196.40