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 $54.95   13.789%   $62.5271   $62.53   $62.55   $62.50  
  Purchase #2 $203.36   4.576%   $212.6658   $212.67   $212.65   $212.70  
  Purchase #3 $224.99   11.227%   $250.2496   $250.25   $250.25   $250.20  
  Purchase #4 $61.28   11.579%   $68.3756   $68.38   $68.40   $68.40  
  Purchase #5 $26.80   8.599%   $29.1045   $29.10   $29.10   $29.10  
  Purchase #6 $193.91   3.430%   $200.5611   $200.56   $200.55   $200.60  
  Purchase #7 $170.35   4.192%   $177.4911   $177.49   $177.50   $177.50  
  7 purchase totals = $935.64       $1,000.9748   $1,000.98   $1,001.00   $1,001.00