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 $24.69   8.783%   $26.8585   $26.86   $26.85   $26.90  
  Purchase #2 $204.58   13.668%   $232.542   $232.54   $232.55   $232.50  
  Purchase #3 $77.79   10.379%   $85.8638   $85.86   $85.85   $85.90  
  Purchase #4 $180.98   4.669%   $189.43   $189.43   $189.45   $189.40  
  Purchase #5 $100.29   12.395%   $112.7209   $112.72   $112.70   $112.70  
  Purchase #6 $229.69   8.317%   $248.7933   $248.79   $248.80   $248.80  
  Purchase #7 $101.92   6.193%   $108.2319   $108.23   $108.25   $108.20  
  7 purchase totals = $919.94       $1,004.4404   $1,004.43   $1,004.45   $1,004.40