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 $164.29   13.508%   $186.4823   $186.48   $186.50   $186.50  
  Purchase #2 $209.51   8.179%   $226.6458   $226.65   $226.65   $226.60  
  Purchase #3 $25.67   13.347%   $29.0962   $29.10   $29.10   $29.10  
  Purchase #4 $174.40   3.143%   $179.8814   $179.88   $179.90   $179.90  
  Purchase #5 $229.29   8.474%   $248.72   $248.72   $248.70   $248.70  
  Purchase #6 $48.94   8.791%   $53.2423   $53.24   $53.25   $53.20  
  Purchase #7 $74.45   3.613%   $77.1399   $77.14   $77.15   $77.10  
  7 purchase totals = $926.55       $1,001.2079   $1,001.21   $1,001.25   $1,001.10