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 $55.92   8.546%   $60.6989   $60.70   $60.70   $60.70  
  Purchase #2 $227.34   7.122%   $243.5312   $243.53   $243.55   $243.50  
  Purchase #3 $79.67   8.201%   $86.2037   $86.20   $86.20   $86.20  
  Purchase #4 $60.49   11.466%   $67.4258   $67.43   $67.45   $67.40  
  Purchase #5 $190.83   5.781%   $201.8619   $201.86   $201.85   $201.90  
  Purchase #6 $55.73   13.474%   $63.2391   $63.24   $63.25   $63.20  
  Purchase #7 $248.96   11.699%   $278.0858   $278.09   $278.10   $278.10  
  7 purchase totals = $918.94       $1,001.0464   $1,001.05   $1,001.10   $1,001.00