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 $87.58   7.302%   $93.9751   $93.98   $94.00   $94.00  
  Purchase #2 $79.87   7.558%   $85.9066   $85.91   $85.90   $85.90  
  Purchase #3 $98.83   9.433%   $108.1526   $108.15   $108.15   $108.20  
  Purchase #4 $215.62   3.332%   $222.8045   $222.80   $222.80   $222.80  
  Purchase #5 $15.97   7.864%   $17.2259   $17.23   $17.25   $17.20  
  Purchase #6 $59.38   6.691%   $63.3531   $63.35   $63.35   $63.40  
  Purchase #7 $238.95   12.148%   $267.9776   $267.98   $268.00   $268.00  
  7 purchase totals = $796.20       $859.3954   $859.40   $859.45   $859.50