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 $56.30   11.168%   $62.5876   $62.59   $62.60   $62.60  
  Purchase #2 $230.40   11.372%   $256.6011   $256.60   $256.60   $256.60  
  Purchase #3 $76.70   3.138%   $79.1068   $79.11   $79.10   $79.10  
  Purchase #4 $231.47   4.731%   $242.4208   $242.42   $242.40   $242.40  
  Purchase #5 $165.66   5.686%   $175.0794   $175.08   $175.10   $175.10  
  Purchase #6 $89.63   8.323%   $97.0899   $97.09   $97.10   $97.10  
  Purchase #7 $49.33   9.236%   $53.8861   $53.89   $53.90   $53.90  
  7 purchase totals = $899.49       $966.7717   $966.78   $966.80   $966.80