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 $92.58   5.764%   $97.9163   $97.92   $97.90   $97.90  
  Purchase #2 $185.86   13.589%   $211.1165   $211.12   $211.10   $211.10  
  Purchase #3 $226.90   11.751%   $253.563   $253.56   $253.55   $253.60  
  Purchase #4 $63.96   7.556%   $68.7928   $68.79   $68.80   $68.80  
  Purchase #5 $38.96   8.451%   $42.2525   $42.25   $42.25   $42.30  
  Purchase #6 $60.88   4.623%   $63.6945   $63.69   $63.70   $63.70  
  Purchase #7 $151.35   10.164%   $166.7332   $166.73   $166.75   $166.70  
  7 purchase totals = $820.49       $904.0688   $904.06   $904.05   $904.10