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 $61.35   12.378%   $68.9439   $68.94   $68.95   $68.90  
  Purchase #2 $91.68   4.352%   $95.6699   $95.67   $95.65   $95.70  
  Purchase #3 $136.44   13.404%   $154.7284   $154.73   $154.75   $154.70  
  Purchase #4 $222.74   12.515%   $250.6159   $250.62   $250.60   $250.60  
  Purchase #5 $125.60   11.253%   $139.7338   $139.73   $139.75   $139.70  
  Purchase #6 $207.79   7.651%   $223.688   $223.69   $223.70   $223.70  
  Purchase #7 $153.32   4.458%   $160.155   $160.16   $160.15   $160.20  
  7 purchase totals = $998.92       $1,093.5349   $1,093.54   $1,093.55   $1,093.50