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 $236.94   12.705%   $267.0432   $267.04   $267.05   $267.00  
  Purchase #2 $184.77   3.833%   $191.8522   $191.85   $191.85   $191.90  
  Purchase #3 $63.88   5.538%   $67.4177   $67.42   $67.40   $67.40  
  Purchase #4 $91.93   3.292%   $94.9563   $94.96   $94.95   $95.00  
  Purchase #5 $99.92   7.353%   $107.2671   $107.27   $107.25   $107.30  
  Purchase #6 $178.44   6.476%   $189.9958   $190.00   $190.00   $190.00  
  Purchase #7 $33.59   3.799%   $34.8661   $34.87   $34.85   $34.90  
  7 purchase totals = $889.47       $953.3984   $953.41   $953.35   $953.50