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 $93.26   6.743%   $99.5485   $99.55   $99.55   $99.50  
  Purchase #2 $223.71   13.414%   $253.7185   $253.72   $253.70   $253.70  
  Purchase #3 $77.45   13.225%   $87.6928   $87.69   $87.70   $87.70  
  Purchase #4 $33.60   3.253%   $34.693   $34.69   $34.70   $34.70  
  Purchase #5 $112.97   6.419%   $120.2215   $120.22   $120.20   $120.20  
  Purchase #6 $214.93   6.644%   $229.2099   $229.21   $229.20   $229.20  
  Purchase #7 $163.80   6.854%   $175.0269   $175.03   $175.05   $175.00  
  7 purchase totals = $919.72       $1,000.1111   $1,000.11   $1,000.10   $1,000.00