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 $76.58   12.553%   $86.1931   $86.19   $86.20   $86.20  
  Purchase #2 $167.40   5.104%   $175.9441   $175.94   $175.95   $175.90  
  Purchase #3 $165.57   7.273%   $177.6119   $177.61   $177.60   $177.60  
  Purchase #4 $62.92   12.259%   $70.6334   $70.63   $70.65   $70.60  
  Purchase #5 $88.63   9.567%   $97.1092   $97.11   $97.10   $97.10  
  Purchase #6 $131.60   13.539%   $149.4173   $149.42   $149.40   $149.40  
  Purchase #7 $50.74   8.524%   $55.0651   $55.07   $55.05   $55.10  
  7 purchase totals = $743.44       $811.9741   $811.97   $811.95   $811.90