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 $60.77   13.193%   $68.7874   $68.79   $68.80   $68.80  
  Purchase #2 $26.69   3.808%   $27.7064   $27.71   $27.70   $27.70  
  Purchase #3 $108.81   11.149%   $120.9412   $120.94   $120.95   $120.90  
  Purchase #4 $79.53   11.481%   $88.6608   $88.66   $88.65   $88.70  
  Purchase #5 $199.93   3.576%   $207.0795   $207.08   $207.10   $207.10  
  Purchase #6 $91.25   5.506%   $96.2742   $96.27   $96.25   $96.30  
  Purchase #7 $232.82   6.770%   $248.5819   $248.58   $248.60   $248.60  
  7 purchase totals = $799.80       $858.0314   $858.03   $858.05   $858.10