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 $239.83   11.640%   $267.7462   $267.75   $267.75   $267.70  
  Purchase #2 $205.78   9.285%   $224.8867   $224.89   $224.90   $224.90  
  Purchase #3 $36.65   12.488%   $41.2269   $41.23   $41.25   $41.20  
  Purchase #4 $26.96   6.163%   $28.6215   $28.62   $28.60   $28.60  
  Purchase #5 $174.63   3.686%   $181.0669   $181.07   $181.05   $181.10  
  Purchase #6 $87.99   7.591%   $94.6693   $94.67   $94.65   $94.70  
  Purchase #7 $26.57   3.344%   $27.4585   $27.46   $27.45   $27.50  
  7 purchase totals = $798.41       $865.6760   $865.69   $865.65   $865.70