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 $87.66   13.173%   $99.2075   $99.21   $99.20   $99.20  
  Purchase #2 $158.69   12.557%   $178.6167   $178.62   $178.60   $178.60  
  Purchase #3 $160.67   9.524%   $175.9722   $175.97   $175.95   $176.00  
  Purchase #4 $87.66   8.688%   $95.2759   $95.28   $95.30   $95.30  
  Purchase #5 $243.29   6.688%   $259.5612   $259.56   $259.55   $259.60  
  Purchase #6 $157.28   5.470%   $165.8832   $165.88   $165.90   $165.90  
  Purchase #7 $183.99   9.483%   $201.4378   $201.44   $201.45   $201.40  
  7 purchase totals = $1,079.24       $1,175.9545   $1,175.96   $1,175.95   $1,176.00